AP Physics Semester 1 MC Answers Study Guide Graded A

AP Physics Semester 1 MC + Answers Study Guide Graded A+ An object is moving to the right with speed vi when a force of magnitude F is exerted on it. In which of the following situations is the object's direction of motion changing & kinetic energy decreasing at the instant shown below: A ball is suspended by a lightweight string, as shown above. The ball is displaced to position 1 and released. The four labeled positions are evenly spaced along the arc of the ball's motion. Between which adjacent pairs of positions is the change in kinetic energy of the ball greatest: A bus is initially traveling north at a constant speed, as shown above. As the bus starts to make a left turn without changing speed, a passenger notices that a box on the floor starts sliding toward the right side of the bus. Which of the following top views of the box, when correctly labeled, would best represent all of the horizontal forces exerted on the box as it starts sliding: Three identical blocks (above) each take a different path from a height h to the ground. Block A is released from rest and falls vertically. Block B is released from rest and slides down a frictionless incline. Block C is projected horizontally with an initial speed v (5 & 6). Which block takes the longest time to reach the ground Which block has the greatest speed just before hitting the ground: A ball is dropped from rest and falls to the floor. The initial gravitational potential energy of the ball Earth-floor system is 10J. The ball then bounces back up to a height where the gravitational potential energy is 7J. What was the mechanical energy of the ball-Earth-floor system the instant the ball left the floor: A 50N box is at rest on a horizontal surface. The coefficient of static friction between the box and the surface is 0.5, and the coefficient of kinetic friction is 0.3. A horizontal 20N force is then exerted on the box. The magnitude of the acceleration of the box is most nearly: Two carts, of mass 2m & m, approach each other head-on with the same speed v as shown above. When the carts collide, they hook together. Assuming positive momentum is to the right, which of the following best represents the momentum of the cart of mass m as a function of time before and after the collision: A student stands at one end of a raft floating in a pool with equally spaced marks along the bottom, as shown above. The student and the raft have the same mass. The student walks to the opposite end of the raft. Which of the following best shows the final locations of the raft and student relative to the marks at the bottom of the pool. Assume that there is no drag force between the raft and the water: Cart A moves horizontally on a frictionless track. It collides and sticks to identical cart B, which is at rest. The speed of cart A before the collision is measured to be 3.0m/s, with an uncertainty of ±0.2m/s. Students are asked to predict the speed of the carts after the collision. Given the uncertainty of the measurement for the speed of cart A, which of the following is the best prediction: A lion is running at constant speed toward a gazelle that is standing still, as shown above. After several seconds, the gazelle notices the lion and accelerates directly toward him, hoping to pass the lion and force him to reverse direction. As the gazelle accelerates toward and past the lion, the lion changes direction and accelerates in pursuit of the gazelle. The lion and the gazelle eventually each reach constant but different speeds. Which of the following sets of graphs shows a reasonable representation of the velocities of the lion and the gazelle as functions of time: A spacecraft of mass 4000kg is traveling in a straight line in the positive direction. Engines can be fired so that the force exerted on the spacecraft is in the positive or negative direction. The graph above shows data for the force during one interval. Which of the following is the best estimate of the net change in the speed of the spacecraft from time t=0 to time t=4s: A rocket is continuously firing its engines as it accelerates away from Earth. For the first km of its ascent, the mass of fuel ejected is small compared to the mass of the rocket. For this distance, which of the following indicates the changes, if any, in the kinetic energy of the rocket, the gravitational potential energy of the Earth-rocket system, and the mechanical energy of the Earth-rocket system: A child slides from rest down slides A and B shown above. The slides are the same height, and the coefficient of friction between the slides and the child is the same. Which of the following compares the change of ∆k in the kinetic energy of the child and the change ∆u in the potential energy of the childEarth system for the two slides: A is shorter slide B is longer (for 17 & 18) A crate is on a horizontal frictionless surface. A force of magnitude F is exerted on the crate at an angle θ to the horizontal, as shown above, causing the crate to slide to the right. The surface exerts a normal force of magnitude FN on the crate. As the crate slides a distance d, it gains an amount of kinetic energy ∆K.While F is kept constant, the angle is now doubled but is still less than 90o. Assume the crate remains in contact with the surface. How does the new normal force exerted on the crate compare to FN: As the crate slides a distance d, how does the new gain in kinetic energy compare to the ∆K holding book against wall FBD The figure above shows the net force exerted on an object as a function of the positon of the object. The objects starts from rest at position x=0 and acquires a speed of 3.0m/s after traveling a distance of 0.090m. What is the mass of the object: Two identical carts are free to move along a straight frictionless track. At time t1, cart X is moving at 2.0m/s when it collides with and sticks to cart Y, which is initially at rest. Which of the following graphs best shows the velocity of cart X before and after the collision: spaceship problem train and balls problem block being pushed down onto spring boxes stacked and force on one another FBD with elevator Ffloor up Fg and Fbox down Assume the elevator has upward acceleration a and consider the stack that has two boxes of mass M. What is the magnitude of the force exerted on the top box by the bottom box: In which of the following situations is the kinetic energy of the object decreasing A 2kg object traveling at 5m/s on a frictionless horizontal surface collides head-on with & sticks to a 3kg object initially at rest. Which of the following correctly identifies the change in total kinetic energy & the resulting speed of the objects after the collision: A stone of mass m is thrown upward at a 30o angle to the horizontal. At the instant the stone reaches its highest point, why is the stone neither gaining nor losing speed: A small cart is rolling freely on an inclined ramp with a constant acceleration of 0.50m/s2 in the -x direction. At time t = 0, the cart has velocity of 2.0m/s in the +x direction. If the cart never leaves the ramp, which of the following statements correctly describes the motion of the cart at a time t 5s FBDs on a slant with a force pulling upward An object's velocity v as a function of time t is given in the graph above. Which of the following statements is true about the motion of the object: A block of mass 10kg moves from position A to position B as shown above. The speed of the block is 10m/s at A & 4.0m/s at B. The work done by friction on the block as it moves from A to B is most nearly: A ladder at rest is leaning against a wall at an angle. Which of the following forces must have the same magnitude as the frictional force exerted on the ladder by the floor Some students want to calculate the work done by friction as an object with unknown mass moves along a straight line on a rough horizontal surface. The students have a force probe, a meterstick, & a stopwatch. Which of the following will allow the students to take the measurements needed to calculate the work done by friction A force F is exerted on a 5kg block to move it across a rough surface, as shown above. The magnitude of the force is initially 5N, & the block moves at a constant velocity. While the block is moving, the force is instantaneously increased to 12N. How much kinetic energy does the block now gain as it moves a distance of 2m Each of the figures above shows a tractor attached to an object. The tractor exerts the same constant force F on each object in every case. Which of the following is a true statement about an object & the relative magnitude of the force exerted by the object on the tractor A cart of known mass moves with known speed along a level, frictionless track, as shown above. The cart hits a force sensor & rebounds. The force sensor measures the force exerted on the cart as a function of time & as a function of the position of the cart. The results will be graphed on the axes shown. Which of the two graphs can be used to determine the cart's speed after it rebounds Two identical blocks are connected to the opposite ends of a compressed spring. The blocks initially slide together on a frictionless surface with velocity v to the right. The spring is then released by remote control. At some later instant, the left block is moving at v/2 to the left, & the other block is moving to the right. What is the speed of the center of mass of the system at that instant A person holds a book at rest a few feet above a table. The person then lowers the book at a slow constant speed & places it on the table. Which of the following accurately describes the change in the total mechanical energy of the Earth-book system A system consists of two spheres, of mass m & 2m, connected by a rod of negligible mass, as shown above. The system is held at its center of mass with the rod horizontal & released from rest near the Earth's surface at time t = 0. Use this for 43 & 44 The graph above shows the rate of change of linear momentum of the sphere of mass m as a function of time. What is the linear momentum of the two-sphere system at time t = 3.0s A person is running on a track. Which of the following forces propels the runner forward In a one-dimensional perfectly elastic collision, an object of mass m is traveling with speed v0 in the + x direction when it strikes an object with mass 3m that is at rest. What are the object's velocities following the collision two people jumping onto rope spaceship other problem kitten problem To analyze the characteristics & performance of the brakes on a 1500kg car, researchers collected the data shown in the table above. It shows the car's speed when the brakes are first applied & the corresponding braking distance required to stop the car. The magnitude of the average braking force on the car is most nearly An ice-skater is moving at a constant velocity across an icy pond. The skater throws a snowball directly ahead. Which of the following correctly describes the velocity of the center of mass of the skater-snowball system immediately after the snowball is thrown? Assume friction & the resistance of air negligible The graph above shows the velocity v as a function of time t for a 0.50kg object traveling along a straight line. The graph has 3 segments labeled 1, 2, & 3. A rope exerts a constant force of magnitude FT on the object along its direction of motion the whole time. During segment 2 only, a frictional force of magnitude Ff is also exerted on the object. FfFt since acceleration is - For another identical object initially at rest, no frictional force is exerted during segment 2 (between t =2s & t = 4s). A rope exerts the same constant force of magnitude FT as in the previous scenario. What is the change in the object's kinetic energy during segment 2 The pendulum shown above reaches a max height h above equilibrium position as it oscillates. Assuming friction & air resistance are negligible, which of the following is true about the total energy of the Earth-pendulum system as the pendulum oscillates A ball of mass m is dropped from rest at height H above the ground from rest and bounces in the positive direction upward to its height H after a perfectly elastic collision with the metal plate on the ground. Which of the following velocity vs time graph best represents the motion of the ba A student is asked to determine the work done on a block of wood when the block is pulled horizontally using an attached string. The student is supplied with a spring scale, a stopwatch, & a meterstick. Which of the following graphical analysis techniques will allow the student to determine the work done on the block by the string Block A & block B move toward each other on a level frictionless track. Block A has mass m & velocity +v. Block B has mass 2m & velocity -v. The blocks collide, & during the collision the magnitude of the net force exerted on block A is F. What is the magnitude of the net force exerted on block B, & why does it have that value The data in the table below were recorded (above) during an experiment in which two carts on a frictionless one-dimensional track collide head-on. What are the values of the magnitude of the change in momentum ∆p2 of cart 2 & the magnitude its average acceleration a2 during the collision A 1.0kg lump of clay is sliding to the right on a frictionless surface with speed 2m/s. It collides headon & sticks to a 0.5kg metal sphere that is sliding to the left with speed 4m/s. What is the kinetic energy of the combined objects after the collision Two identical blocks with mass 5.0kg each are connected to the opposite ends of a compressed spring. The blocks initially slide together on a frictionless surface with velocity 2m/s to the right. The spring is then released by remote control. At some later instant, the left block is moving at 1m/s to the left, & the other block is moving to the right. What is the speed of the center of mass of the system at that instant The graph above shows the position x as a function of time for the center of mass of a system of particles of total mass 6.0kg. For a very short time interval around 2.0s, an external force is exerted on an object in the system. What is the resulting change in momentum of the system Using a force probe, a student generates the graph above of the force exerted on a small wagon as a function of time. The wagon starts from rest & rolls with negligible friction on the axles. Which of the following graphs best represents the wagon's momentum as a function of time: A 0.050kg tennis ball is moving to the left at 10m/s when it is hit by a racket that is moving to the right. The magnitude of the force exerted on the ball by the racket as a function of time is shown above. What is the speed of the ball after the collision with the racke An object starts from rest & slides with negligible friction down an air track tipped at an angle θ from the horizontal. A student records values of the object's position along the track at various times. The value of θ can best be determined from which of the following Box A of mass m sits on the floor of an elevator, with box B of mass 2m on top of it, as shown above. The elevator is moving upward & slowing down. FA is the magnitude of the force exerted on box A by box B, FB is the magnitude of the force exerted on box B by box A, & Fg is the magnitude of the gravitational force exerted on box B. Which of the following ranks the forces in order of increasing magnitude The inclined plane in the figure above has two sections of equal length & different roughness. The dashed line shows where the section 1 ends & section 2 begins. A block of mass M is placed at different locations on the incline. The coefficients of kinetic & static friction between the block & each section are shown in the table below. If the block is at rest on section 1 of the incline, what is the magnitude of the force of static friction exerted on the block by the incline kinetic friction Us=1/2kx^2 A blue sphere & a red sphere with the same diameter are released from rest at the top of a ramp. The red sphere takes a longer time to reach the bottom of the ramp. The spheres are then rolled off a horizontal table at the same time with the same speed & fall freely to the floor. Which sphere reaches the floor first A 12kg box sliding on a horizontal floor has an initial speed of 4.0m/s. The coefficient of friction between the box & the floor is 0.20. The box moves a distance of 4.0m in 2.0s. The magnitude of the change in momentum of the box during this time is most nearly A sled slides down a hill with friction between the sled & the hill but negligible air resistance. Which of the following must be correct about the resulting change in energy of the sled-Earth system An object is moving to the west at a constant speed. Three forces are exerted on the object. One force is 10N directed due north, & another is 10N directed due west. What is the magnitude & direction of the third force if the object is to continue moving to the west at a constant speed Block A of mass 2.0kg is released from rest at the top of a 3.6m long plane inclined at an angle of 30.o, as shown above. After sliding on the horizontal surface, block A hits & sticks to block B, which is at rest & has mass 3.0kg. Assume friction is negligible. The speed of the blocks after the collision is most nearly A student is asked to move a box from ground level to the top of a loading dock platform, as shown in the figures above. In Figure 1, the student pushes the box up an incline with negligible friction. In Figure 2, the student lifts the box straight up from ground level to the loading dock platform. In which case does the student do more work on the box, & why A student uses a spring scale to exert a horizontal force on a block, pulling the block over a smooth floor. The student repeats the procedure several times, each time pulling the block from rest through a distance of 1.0m. For which of the following graphs of force as a function of distance will the block be moving the fastest at the end of the 1.0m A projectile fired into the air explodes & splits into two halves of equal mass that hit the ground at the same time. If the projectile had not exploded, it would have landed at point X, which is a distance R to the right of the launch point. After the explosion, one of the halves lands at point Y, which is a distance 2R to the right of the launch point. If air resistance is negligible, where did the other half land An elevator carrying a person of mass m is moving upward & slowing down. How does the magnitude F of the force exerted on the person by the elevator floor compare with the magnitude mg of the gravitational force A soft foam block of mass m slides without friction in the positive x-direction with speed v. At time t = 0, a student briefly pushes the block with a force probe in the positive x-direction. The graph above shows the force probe's measurements as a function of time during the push. Which of the following statements is true about the block's momentum between t = 0 & t = t1 A cart is moving on a level track in the positive x-direction. A force acting parallel to the x-axis is exerted on the cart. The graph above shows the net force exerted on the cart as a function of displacement. As the cart travels from x = 0m to x = 4m, what is the net change in the kinetic energy of the cart Two objects, A & B, move toward one another. Object A has twice the mass & half the speed of object B. Which of the following describes the forces the objects exert on each other when they collide & provides the best explanation A 1.0kg block is attached to an unstretched spring of spring constant 50.N/m & released from rest from the position shown in Figure 1 above. The block oscillates for a while & eventually stops moving 0.20m below its starting point, as shown in Figure 2. What is the change in potential energy of the block-spring-Earth system between Figure 1 & Figure 2 Blocks A & B, of masses mA & mB, are at rest on a frictionless surface, as shown above, with block A fixed to the table. Block C of mass mC is suspended by a string that is tied to block B over an ideal pulley. Which of the following gives the magnitude of the force exerted by block A on block B A cart of mass m is moving with negligible friction along a track with known speed v1 to the right. It collides with and sticks to a cart of mass 4m moving with known speed v2 to the right. Which of the two principles, conservation of momentum & conservation of mechanical energy, must be applied to determine the final speed of the carts, & why In a classroom at time t = 0, a sphere is thrown upward at a 45o angle to the horizontal. At time t1, while the sphere is still rising, it bounces off the ceiling elastically & with no friction. Which of the following pairs of graphs could represent the sphere's horizontal velocity & vertical velocity as functions of time t: block with Force down and to the left--- move vector to draw triangle correctly F vs spring length slope is k A block of known mass hanging from an ideal spring of known spring constant is oscillating vertically. A motion detector records the position, velocity, and acceleration of the block as a function of time. Which of the following indicates the measured quantities that are sufficient to determine whether the net force exerted on the block equals the vector sum of the individual forces Block a hangs from a light string that passes over a light pulley and is attached to block B, which is on a level horizontal frictionless table, as shown above. Students are to determine the mass of block B from the motion of the two-block system after it is released from rest. They plan to measure the time block A takes to reach the floor. The students must also take which of the following measurements to determine the mass of block B Two blocks, of mass m and 2m, are initially at rest on a horizontal frictionless surface. A force F is exerted individually on each block, as shown above. The graph shows how F varies with time t. Which block has the greatest average power provided to it between t=0s and t=3s with graph of 2 lines becoming one Which block has the greater mass, and what information indicates this How does the kinetic energy of the two-block system after the collision compare with its kinetic energy before the collision, and why Which is true of the motion of the center of mass of the two-block system during the time shown book against wall problem cart with spring A block of mass m is at rest on a rough incline, as shown in the figure above. Which of the following forces must have a magnitude equal to mg?