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NSCI 101-001 Chapter: 4
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NSCI 101-001 Chapter: 4
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NSCI 101-001 Chapter: 4You exert a force on a ball when you toss it upward. How long does that force last
after the ball leaves your hand? - ANSWER The force you exert on the ball ceases
as contact with your hand ceases
On a long alley, a bowling ball slows down as it rolls. Is any horizontal force acting
on the ball? How do you know? - ANSWER Yes, if the ball slows down, a force
opposite to its motion is acting - likely air resistance and friction between the ball and
the alley.
If a motorcycle moves with a constant velocity, can you conclude that there is no net
force acting on it? How about with constant acceleration? - ANSWER Constant
velocity means zero acceleration, so yes, no net force acts on the motorcycle but
when moving at constant acceleration there is a net force acting on it.
Since an object's weighs less on the surface of the moon than on the Earth's
surface, does it have less inertia on the moon's surface? - ANSWER No, inertia
involves mass not weight.
Which contains more apples: a 1-pound bag of apples on Earth or a 1-pound bag of
apples on the Moon? Which contains more apples: a 1-kilogram bag of apples on
Earth or a 1-kilogram bag of apples on the moon? - ANSWER Items like apples
weigh less on the moon, so there are more apples in a 1-pound bag of apples there.
Mass is another matter, for the same quantity of apples are in 1-kg bag on the Earth
and on the Moon.
If gold were sold by weight, would you rather buy it in Denver or Death Valley? If it
were sold by mass, which of these locations makes the best buy? Defend your
answers. - ANSWER Buy by weight in Denver because the acceleration of gravity is
less in Denver than in Death Valley. Buying by mass would be the same amount in
both locations.
In an orbiting space vehicle, you are handed two identical boxes, one filled with sand
and the other filled with feathers. How can you determine which is which without
opening the boxes? - ANSWER Shake the boxes. The box that offers the greater
resistance to acceleration is the more massive box, the one containing the sand.
Your empty hand does not hurt when it bangs lightly against a wall. Why does it hurt
if you're carrying a heavy load? Which of Newton's laws is most applicable here? -
ANSWER When you carry a heavy load there is more mass involved and a greater
tendency to remain moving. If a load in your hand moves toward a wall, its tendency
is to remain moving when contact is made. This tends to squash your hand if it is
between the load and the wall-an unfortunate example of Newton's first law in action.
Does the mass of an astronaut change when he or she is visiting the International
Space Station? Defend your answer. - ANSWER Mass is a measure of the amount
, of matieral in something, not gravitational pull depends on its location. So although
the weight of the astronaut may change with location, mass does not.
Why does a massive cleaver more effective for chopping vegetables than and
equally sharp knife? - ANSWER A massive cleaver is more effective in chopping
vegetables because its greater mass contributes to greater tendency to keep moving
as the cleaver chops the food.
When a junked car is crushed into a compact cube, does its mass change? Its
weight? Explain. - ANSWER Neither the mass nor the weight of a junked car
changes when it is crushed. What does change is its volume, not to be confused with
mass and weight.
Gravity on the surface of the Moon is only 1/6 as strong as gravity on Earth. What is
the weight of a 10-kg object on the Moon and on the Earth? What is its mass on
each? - ANSWER 10 kilograms weight about 100 N on the Earth (weight = mg =
10kg X 10 m/s^2 = 100 N or 98 N if g = 9.8 m/s^2 is used) On the moon the weight is
1/6 of 100 N = 16.7 N (or 16 N if g = 9.8 m/s^2 is used). The mass is 10 kg
everywhere.
What happens to the weight reading on a scale you stand on when you toss a heavy
object upward? - ANSWER The scale reading will increase during the throw. Your
upward force on the heavy object is transmitted to the scale.
What weight change occurs when your mass increases by 2 kg? - ANSWER The
change of weight is the change of mass times g, so when mass changes by 2 kg,
weight changes by about 20 N.
A grocery bag can withstand 300 N of force before it rips apart. How many kilograms
of apples can it safely hold? - ANSWER A 1-kg mass weighs 10 N, so 30 kg weighs
300 N. The bag can safely hold 30 kg of apples - if you don't pick it up too quickly.
A crate remains at rest on a factory floor while you push on it with horizontal force, F.
What is the friction force exerted on the crate by the floor? Explain. - ANSWER Since
the crate remains at rest, the net force on it is zero, which means the force of friction
by the floor on the crate will be equal and opposite to your applied force.
Explain how Newton's first law of motion can be considered to be a consequence of
Newton's second law. - ANSWER The second law states the relationship between
force and acceleration. If there is no net force, there is no acceleration-which is what
Newton's first law states. So Newton's first law is consistent with the second law, and
can be considered to be a special case of the second law.
When a car is moving in reverse, backing out of a driveway, the driver applies the
breaks. In what direction is the car's acceleration? - ANSWER Acceleration (slowing
of the car) is opposite to velocity (Direction the car is moving).
Aristotle claimed that the speed of a falling object depends on its weight. We now
know that objects in free, whatever the gravitational forces on them, undergo the
same gain in speed. Why don't differences in their gravitational forces affect their
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