ย 
โ† PREVIOUS TOPIC
LOADING FULL SCREEN

Energy stores for Edexcel A-level Physics

Energy stores

This page covers the following topics:

1. Gravitational potential energy
2. Elastic strain energy
3. Kinetic energy

Gravitational potential energy refers to the energy possessed by an object due to its position above the ground. It can be calculated by multiplying the mass of an object, gravitational field strength and height the object has been lifted to. Gravitational field strength on the surface of the Earth is commonly approximated to be 9.81 m/sยฒ.

Gravitational potential energy

All the work done in stretching or compressing an elastic object is stored as elastic strain energy, which is equivalent to the elastic potential energy. The elastic strain energy in J can be calculated using E = 1/2 ร— F ร— x, where F is the force that is causing the stretching or compressing of the object in N, and x is the extension in m. This energy is equivalent to the area under a force-extension graph.

Elastic strain energy

Kinetic energy is the energy an object has due to its motion and thus its speed. It can be calculated using E = 1/2 ร— mass ร— velocityยฒ and is given in joules, J. A moving vehicle can be stopped only when work is done on it which is equivalent to the kinetic energy the vehicle possesses.

Kinetic energy

1

Kate drops a 275 g volleyball towards the ground. Given that when the ball is 0.5 m above the ground the change in gravitational potential energy is 2.7 J, calculate the height above the ground at which the ball is dropped from. Use g = 9.81 N/kg.

E = mgh
2.7 J = 0.275 kg ร— 9.81 N/kg ร— change in height
change in height = 2.7 J/(0.275 kg ร— 9.81 N/kg) = 1.00 m (3 s. f.)
height above the ground initially = 0.5 m + 1.00 m = 1.5 m

1.5 m

Kate drops a 275 g volleyball towards the ground. Given that when the ball is 0.5 m above the ground the change in gravitational potential energy is 2.7 J, calculate the height above the ground at which the ball is dropped from. Use g = 9.81 N/kg.

2

Calculate the gravitational potential energy stored in a tennis ball of mass 60 g that is held 1.4 m above the ground. Use g = 9.81 N/kg.

E = mgh
E = 0.06 kg ร— 9.81 N/kg ร— 1.4 m = 0.82 J

0.82 J

Calculate the gravitational potential energy stored in a tennis ball of mass 60 g that is held 1.4 m above the ground. Use g = 9.81 N/kg.

3

A spring is stretched by 10 cm using a force of 10 N. Calculate the elastic strain energy stored in the spring.

E = (1/2)Fx
E = (1/2) ร— 10 N ร— 0.1 m = 0.5 J

0.5 J

A spring is stretched by 10 cm using a force of 10 N. Calculate the elastic strain energy stored in the spring.

4

A biker is driving his bike of mass 10 kg at a speed of 7.2 m/s. Given that the kinetic energy of the bike and biker is 1763 J, calculate the mass of the biker.

E = 0.5mvยฒ
Let m be the biker's mass.
1763 J = 0.5 ร— (m + 10 kg) ร— (7.2 m/s)ยฒ
m = (2 ร— 1763) รท 7.2ยฒ โˆ’ 10 = 58 kg

58 kg

A biker is driving his bike of mass 10 kg at a speed of 7.2 m/s. Given that the kinetic energy of the bike and biker is 1763 J, calculate the mass of the biker.

5

Given that the mass of a runner is 62 kg and that she is running at a speed of 11 m/s, find the kinetic energy of the runner.

E = 0.5mvยฒ
E = 0.5 ร— 62 kg ร— (11 m/s)ยฒ = 3751 J

3751 J

Given that the mass of a runner is 62 kg and that she is running at a speed of 11 m/s, find the kinetic energy of the runner.

End of page

ย