The principle of conservation of energy states that the total amount of energy at the end of a process is always the same as the total amount of energy at the beginning.

Friction or air resistance can cause energy to dissipate into the surroundings as heat.

The energy an object has in its gravitational store is referred to as the object’s gravitational potential energy.

The energy an object has in its kinetic store is referred to as the object’s kinetic energy.

Calculating energy changes (Ek and Ep)

Physics

In the Forces make things change unit, they will build on this knowledge to learn how to combine forces in two dimensions, how to calculate acceleration from a resultant force and how to calculate forces in collisions and explosions.

In the Measuring and calculating motion unit, pupils learnt how to measure and calculate velocity and acceleration, and how to interpret displacement-time and velocity-time graphs. 

Energy of moving objects

The principle of {{}} states that total amount of energy at the end of a process is always the same as the total amount of energy at the beginning.

1600 J is transferred from the kinetic to the gravitational store.

1600 J is transferred from the gravitational to the kinetic store.

Less than 1600 J is transferred from the gravitational to the kinetic store.

More than 1600 J is transferred from the gravitational to the kinetic store.

More than 1600 J is transferred from the kinetic to the gravitational store.

A rock on a cliff has 1600 J of energy in the gravitational store. It falls off the cliff onto the ground below. During the fall, no energy is dissipated. What is the energy transfer during the fall?

A 0.20 kg ball is thrown straight upwards and reaches a maximum height of 2.1 m. The ball’s kinetic energy at the start is {{}} J. (Assume no energy is dissipated. Use $$g$$ = 10 N/kg.)

It is impossible to say whether the final speed will be more or less than 4 m/s.

A plate is dropped. If no energy is dissipated during the fall, the final speed of the plate before it hits the ground is 4 m/s. If energy is dissipated, which of these statements is correct?

A child sledges down a hill of height 12 m. The total mass of child and sledge is 30 kg. At the bottom, the kinetic energy is {{}} J. (Assume no energy is dissipated. Use $$g$$ = 10 N/kg.)

A mountain goat with mass 52 kg jumps straight upwards, leaving the ground at speed 6.0 m/s. The maximum height it can reach is {{}} m. (Use $$g$$ = 10 N/kg.)

Match each symbol in the equations $$E_p = mgh$$ and $$E_k = ½mv^2$$ with the quantity it represents.

The kinetic energy of an object is directly proportional to its mass.

The kinetic energy of an object is directly proportional to its speed.

Gravitational potential energy is directly proportional to an object's mass.

Gravitational potential energy is directly proportional to an object’s speed.

An eagle with mass 4.0 kg flies at speed 15 m/s. How much energy is in its kinetic store?

A book of mass 1.6 kg falls off a shelf onto the floor. The shelf is 2.0 m above the floor. What is the change in energy in the gravitational store? (Use $$g$$ = 10 N/kg.)

An apple of mass 200 g falls from a branch that is 150 cm above the ground. What is the change in energy in the gravitational store? (Use $$g$$ = 10 N/kg.)

Starter Quiz