PHYSICAL SCIENCES 1/2
Physics focus
GRADE 11
November 2023
These notes were compiled using past exam papers: SACAI JUN & NOV 2019/2020/2021
Short questions
Newton's first law The law explains why a spacecraft can move through space at a
constant speed without using any fuel.
Mass and distance Two factors that affect the gravitational attraction between two
objects are mass and distance
Huygens' principle The principle or law that states that every point on a wavefront can be
seen as a source for a new wave is Huygens' principle.
The vector diagram represents three forces acting simultaneously on
an object moving at a CONSTANT VELOCITY
In the circuit diagram below, the internal resistance of the battery and
the resistance of the conductors are negligible. The emf of the battery
is E. When switch S is closed, the reading on the voltmeter is V, in volts
The diagram shows a magnet moving into a coil, the polarity of Y is
South.
, The figure shows a small, positively charged polystyrene ball hanging
from a wooden beam. Due to the electrostatic force
acting on it, the ball is displaced from its original
vertical position. It comes to rest when the hanging
wire makes an angle with the vertical, as indicated in
the figure.
The free-body diagram best describes the direction of
the forces acting on the ball in this position.
A person stands on a scale in an elevator that is initially stationary. The
elevator accelerates upward, continues at a constant speed, and then
slows down until it stops.
1.0 X 103 N When a basketball player, weighing 5.0 x 102 N, jumps up from the
floor to the basket ('basket') the magnitude of the force exerted by her
feet on the floor is 1.0 x 103 N. When she jumps then the magnitude of
the force exerted by the floor on her feet
The diagram shows a block experiencing two opposing forces. There is
no frictional force between the block and the surface. The acceleration
of the block will be to the right.
The relationship between the magnitude of the block's gravitational
force, Fg and the Normal force, FN is, Fg > FN.
The net force, in Newtons, acting on the block is Fnet = 200 – 200 cos
30°.
The block accelerates to the
left. Take 'to the left' as
positive.
Learners investigate the relationship between current (I) and potential
difference (V) at a constant temperature for three different resistors,
X, Y and Z.
The resistances of X, Y and Z are RX, RY and RZ respectively
Conclusion about the resistance= Rz > RY > Rx
A student pulls a block at a CONSTANT SPEED across a rough horizontal
surface with a horizontal force F. The force diagram below shows all
the forces acting on the block.
F = Y and X = Z
Two charged spheres, A and B, are placed on insulated stands at a
distance r from each other, as shown below. The magnitude of the
electrostatic force between the spheres is F.
The spheres are allowed to touch each other and are returned to their
original positions. The magnitude of the electrostatic force in terms of
F is now
, Three identical light bulbs X, Y and Z are connected in a circuit as
shown. The internal resistance of the battery is negligible. When
switch S is closed, the reading on ammeter A1 is 2.5 A.
Description of the readings on the ammeters (in amperes) when bulb Z
burns out.
A1 = 1.8
A2 = 1.8
A3 = 0
Acceleration A constant, resultant force acts on a body that is free to move in a
straight line. This physical quantity remains constant.
A man stands on a bathroom scale in an elevator. The man weighs 65 kg. The
reading on the scale is 650 N . The elevator accelerates upward to obtain this
reading on the bathroom scale.
A person stands on a bathroom scale, calibrated in newtons, in a stationary elevator. The reading on
the bathroom scale is W. The elevator is now moving at a constant acceleration of g upwards, where
g is the gravitational acceleration. What will the reading on the bathroom scale be now?
w
An object is dropped from a height 7 km above the earth's surface. If air resistance is ignored, the
acceleration of the object depends on the radius of the earth at that point.
An insect hits the windshield of a moving vehicle. Compared to the magnitude
of the force exerted by the insect on the pane, the force exerted by the pane
on the insect will be the same.
The driver of a car takes a block and places it on the dashboard in front of him. After a while he finds
the block sliding in his direction. What kind of movement will it cause? The car accelerates forward.
The optical density of a medium is an indication of the refractive power of the medium
The diagram shows a car towing a trailer.
The force applied by the trailer on the car is equal to the force applied by the car on the trailer to the
right.
A ray of light strikes the surface between water and air at a right angle. The frequency of the light will
remain constant.
The weight of a man on the Earth's surface is w. Planet X has the same radius as Earth, but half the
mass of Earth. The weight of the man on Planet X's surface would be ½ w.
,The mass of a person on Earth is 75 kg. Its mass and weight on the moon, with a gravitational
acceleration of 1.67 ms-2 , would be
Mass on the moon in kg = 75kg
Weight on the moon in N = 125.25
The force of attraction between two bodies is F if they are a distance r apart. The bodies move until
the force between them is 16 F. The distance between the two bodies is now
The diagram shows water waves in the same plane spreading out as they pass through a single spike.
The wave phenomenon that is observed when the water waves travel through the single slit is
diffraction.
,You may find similar questions in the exam, try to answer them yourself without looking at the
answers.
Mechanics
Question(SACAI JUN 2019)
The diagram below shows how a heavy object is lifted using two ropes (ignore their masses) and
frictionless pulleys. Force FA in rope A is 730 N and force FB in rope B is 1440 N. Rope A makes an
angle of 70o with the horizontal while B makes an angle of 10o with the vertical.
Object
The resultant of two or more forces= Single force that has the same effect as two or more forces
together.
Calculate the vertical components of strings A and B.
, Calculate the horizontal components of strings A and B
Calculate the maximum mass of the object that can be lifted with this system.
Question (SACAI NOV 2020)
The helicopter below, with a mass of 2 tons, saves a man. The man hangs motionless on the rope as
shown below.
A rope connects to the helicopter and there is a tension of 882 N in the rope. The rope cannot stretch
and the mass of the rope can be ignored.
Calculate the mass of the man.
T = Fg
, The helicopter lowers the man into a boat.
The man moves downward with an acceleration of 0.22 ms -2 while the helicopter remains in
position, with the rotor blades still moving at the same speed.
Calculate the tension in the rope as the man is lowered.
Newton's third law of motion
The force A exerts on B is just as great as the force B exerts on A, just in opposite directions.
The action-reaction power couple on the man
The force that the man exerts on the rope (downwards due to gravity) and the force that the rope
exerts on the man (upwards).
Question (SACAI Nov 2020)
The figure below represents a ramp used for wheelchairs and trolleys. The ramp must be a minimum
of 5 m in length and make an angle of 3.6° with the horizontal. The combined mass of the trolley and
its contents is 70 kg. The coefficient of static friction between the wheels of the trolley and the ramp
is 0.08. Once the trolley starts moving, it drops to 0.06.
Static friction= The static friction force, fs, is the force that opposes the tendency of motion of a
stationary object relative to the surface.
Can you draw a free-body diagram of all the forces acting on the trolley?Try yourself.
