Calculating the energy of moving objects (Ek=1/2mv2) | Exit Quiz | Oak National Academy

How much energy will be transferred to the kinetic store if three times the amount of work is done on kicking a football?

• The same amount of energy.

• Three times as much energy.

• Nine times as much energy.

Answer explanation

Work done is equal to the amount of energy transferred, so doing three times the amount of work transfers three times the amount of energy to the football and into the kinetic store.

If friction and air resistance are ignored, how much energy is dissipated by a toy car moving across a table?

• All of the car's energy.

• Most of the car's energy.

• A tiny amount of the car's energy.

• None of the car's energy.

Answer explanation

No energy dissipates if there is no friction or air resistance because there would be no friction to transfer energy to the thermal store and air particles would not be pushed out of the way.

What happens to the amount of energy in the kinetic store of a ball if it is moving at two times the speed?

• The amount of energy in the kinetic store does not change.

• The amount of energy in the kinetic store is two times bigger.

• The amount of energy in the kinetic store is four times bigger.

Answer explanation

Four times the work is needed to make a ball move at two times the speed. A ball travelling at two times the speed has four times the amount of energy in the kinetic store.

What is kinetic energy?

• The type of energy that is in the kinetic store.

• The type of energy an object has because it is moving.

• The amount of energy an object has that is in its kinetic store.

• The total amount of energy that a moving object has.

Answer explanation

The kinetic energy of an object is the amount of energy it has in the kinetic store. It may also have energy in other stores such as the thermal store and the gravitational store.

What is the kinetic energy of a discus of mass 2 kg moving at a speed of 8 m/s?

What is the mass of a javelin that has a kinetic energy of 72 J and a speed of 12 m/s?

Answer explanation

72 J = ½ × m × (12 m/s × 12 m/s) 72 = 72 × m m = 1 kg