Energy and Work Done

The Principle of Conservation of Energy states that energy cannot be created or destroyed, it can only be transferred from one form to another. The total amount of energy remains constant.

• True

• False

Which of the following shows the correct formulae for gravitational potential energy E_p and kinetic energy E_k? 

A cyclist pedals to the top of a hill at constant speed.

Which type of energy decreases as he pedals?

• chemical potential energy.

• elastic potential energy

• gravitational potential energy

• kinetic energy

A car is travelling along a level road.

The brakes are applied and the car slows down and stops.

Which form of energy is most of the car's kinetic energy converted to?

• chemical potential energy

• gravitaional potential energy

• sound

• thermal

Two balls of equal mass are dropped from the same height, h, down frictionless pipes that reach the ground. One pipe is straight while the other is curved as shown.

Which statement is true of the kinetic energy of the two balls as they emerge from the pipes?

• KE (ball K) > KE (ball L)

• KE (ball K) < KE (ball L)

• KE (ball K) = KE (ball L)

A ball of mass 2.0kg rolls down the hill. At 2.0m above the ground, it is travelling at a speed of 3.0m/s.

What is the kinetic energy of the ball at the bottom of the hill?

(Take the gravitational field strength as 10 N/kg and ignore any effects of friction).

• 9.0J

• 40J

• 43J

• 49J

A 2.0kg ball is at a height of 6m above ground.

Calculate the gravitational potential energy that it has.

• 12J

• 120J

Calculate the work done to lift a 2.0kg ball 6m above ground.

• 12J

• 120J

The 2.0kg ball falls 4.0m to it current height of 2.0m above ground.

Calculate the decrease in the ball's graviational potential energy.

• 4.0J

• 8.0J

• 40J

• 80J

The 2.0kg ball falls 4.0m to it current height of 2.0m above ground.

State the kinetic energy of the 2.0kg ball at this height.

• 4.0J

• 8.0J

• 40J

• 80J