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 - with complex examples (E)

Combined science

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.

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 the following statements is correct?

A 0.20 kg ball is thrown vertically upwards and reaches a maximum height of 2.1 m. 
Assuming that no energy is dissipated, the ball’s kinetic energy at the start is {{}} J.
Use $$g$$ = 10 N/kg.

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

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

A frog with a mass of 0.025 kg jumps vertically upwards and reaches a height of 0.40 m. 
Which of the following is the frog’s speed at the moment it jumps? 
Use $$g$$ = 10 N/kg.

gravitational potential energy or kinetic energy

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

Match the following quantities to their units.

Kinetic energy is directly proportional to an object's mass.

Kinetic energy is directly proportional to an object's speed.

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

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

Which of the following statements are correct?

An eagle with a mass 4.0 kg flies at a speed 15 m/s. 
Which of the following is the amount of energy 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. 
Which of the following 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. 
Which of the following is the change in energy in the gravitational store? 
Use $$g$$ = 10 N/kg.

Starter Quiz