Kognity Classwork Semester 2

An object of mass m is initially at rest. An impulse I acts on the object. The change in kinetic energy of the object is

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A body moving along a straight-line has mass 3.0 kg and kinetic energy 24 J. The motion is then opposed by a net force of 4.0 N. The body will come to rest after travelling a distance of

• 2.0m

• 6.0m

• 8.0m

• 12m

The point of action of a constant force F is displaced a distance d. The angle between the force and the direction of the displacement is θ, as shown below.

Which one of the following is the correct expression for the work done by the force?

• Fd

• Fd sin θ

• Fd cos θ

• Fd tan θ

The diagram below represents energy transfers in an engine.

The efficiency of the engine is given by the expression

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The variation with time of the vertical speed of a ball falling in air is shown below.

During the time from 0 to T, the ball gains kinetic energy and loses gravitational potential energy ΔEp. Which of the following statements is true?

• ΔEp is equal to the gain in kinetic energy.

• ΔEp is greater than the gain in kinetic energy.

• ΔEp is equal to the work done against air resistance.

• ΔEp is less than the work done against air resistance.

The diagram below shows a 50 kilogram crate on a frictionless plane at angle to the horizontal. The crate is pushed at constant speed up the incline from point A to point B by force F.

If angle were increased, what would be the effect on the magnitude of force F and the total work W done on the crate as it is moved from A to B?

• W would remain the same and the magnitude of F would decrease. 


• W would remain the same and the magnitude of F would increase. 


• W would increase and the magnitude of F would decrease.

• W would increase and the magnitude of F would increase.

A man standing on a scale in an elevator notices that the scale reads 30 N greater than his normal weight. Which type of movement of the elevator could cause this greater-than-normal reading?

• accelerating upward


• accelerating downward


• moving upward at constant speed

• moving downward at constant speed

A 60 kg skydiver is falling at a constant speed near the surface of Earth. The magnitude of the force of air friction acting on the skydiver is approximately 


• 0N

• 6N

• 60N

• 600N

When a 12 N horizontal force is applied to a box on a horizontal tabletop, the box remains at rest. The force of static friction acting on the box is

• 0 N


• between 0 N and 12 N

• 12 N


• greater than 12 N

Ball A of mass 5.0 kg moving at 20 ms-1 collides with ball B of unknown mass moving at 10ms-1 in the same direction. After the collision, ball A moves at 10 ms-1 and ball B at 15ms-1, both still in the same direction. What is the mass of ball B? 


• 6.0 kg

• 2.0 kg

• 10 kg

• 12 kg