Practise Questions

Question 1

David pushes his 800kg car for 5.0 metres with a force of 920N. How much work does he do?

Answer 1

Work done= Force x Distance

W= 920 x 5 = 4600J

Question 2

David pushes his 800kg car for 5.0 metres with a force of 920N. How much energy is transferred to the car and which store is it transferred to?

Answer 2

4600J to the Kinetic Store.

920 x 5 energy is inputed, so 4600J must be outputted. Energy can never “vanish.”

Question 3

David pushes his 800kg car for 5.0 metres with a force of 920N. How fast is the car moving when David finishes pushing?

Answer 3

Ek = (mv^2) /2
Now make v the subject:
2Ek = mv^2
2Ek / m = v^2

=Square root of 2Ek / m = v
Input variables:
Ans= 3.16m/s

Question 4

A 70kg stunt man falls 8 metres into an airbag before stopping. How much energy is in the stunt man’s gravitational potential store before they jump?

Answer 4

Eg = mgh
70 x 9.8 x 8 = 5488J

Question 5

A 70kg stunt man falls 8 metres into an airbag before stopping. How much energy is transferred to their kinetic store just before they hit the airbag?

Answer 5

5488J
70 x 9.8 x 8
Energy in = Energy out

Question 6

A 70kg stunt man falls 8 metres into an airbag before stopping. How much work needs to be done to stop the stunt man?

Answer 6

The work done by the airbag to stop him must equal this kinetic energy.

The work needed to stop the stuntman is equal to the gravitational potential energy lost during the fall. Therefore: the work required to stop the stuntman is 5488 joules.