Physics Prep

A designer wants to improve the stability of a tall streetlight during storms. What design change would best achieve this?

• Lowering the position of its centre of gravity
• Making the base narrower
• Adding decorative elements near the top
• Using lighter materials only at the base

Answer explanation

A low centre of gravity increases stability and reduces the risk of toppling.

Two ice skaters push off from each other on frictionless ice. Which statement is true?

• Both skaters' momenta change, but total momentum remains constant
• Both skaters' velocities remain unchanged
• The total kinetic energy must be conserved
• Each skater has the same momentum after they push apart

Answer explanation

Momentum is conserved in isolated systems; individual momenta can change.

A trolley of mass 3 kg moving at 4 m/s hits a bumper and stops in 1.5 s. What is the average force applied by the bumper?

• 2 N
• 4 N
• 8 N
• 12 N

Answer explanation

Force = change in momentum / time = (3×4)/1.5 = 8 N.

A cricket ball of mass 0.16 kg moves at 20 m/s. What are the correct units of its momentum?

• kg m s⁻¹
• kg s⁻¹
• N m
• N s

Answer explanation

Momentum = mass × velocity; so units = kg × m/s = kg m s⁻¹.

Which measurement shows exactly three significant figures?

• 0.00540 m
• 40.20 kg

• 3000 cm
• 6.789 V

Answer explanation

0.00540 has 3 significant figures: 5, 4, and the trailing 0.

Two students pull on opposite ends of a rope with forces of 60 N and 45 N. What force and direction would balance the rope?

• 105 N opposite to 60 N
• 15 N opposite to 60 N
• 15 N opposite to 45 N
• 105 N opposite to 45 N

Answer explanation

A 15 N force opposite the larger force balances the net force.

The turning effect of a force about a point is called:

• moment

• inertia
• energy
• thrust

Answer explanation

Torque or moment is the turning effect of a force.

The distance-time graph for a cyclist shows a horizontal line. What does this mean?

• The cyclist is stationary
• The cyclist is speeding up
• The cyclist is slowing down
• The cyclist moves at a constant speed

Answer explanation

A horizontal distance-time graph indicates no change in distance—stationary.

A scientist measures the diameter of a small wire as 0.00786 m. What is this value expressed to 2 significant figures?

• 0.0079 m
• 0.0078 m
• 0.00786 m
• 0.007 m

Answer explanation

0.00786 rounded to 2 significant figures is 0.0079 (7 and 9 are significant).

A ball thrown straight up reaches point X where its velocity is zero. What does point X represent?

• The highest point in its path
• The moment it hits the ground
• The point it was released
• The start of its descent

Answer explanation

Velocity is zero at the highest point in vertical motion.