In order to fill the tank completely the pump would’ve had to lift 45 L of petrol by 4m.

We can calculate this using the gravitational potential energy formula:

E = mgh where m is the mass, g is acceleration due to gravity and h is the height difference.

Since the question told us that 1 litre of petrol weighs 6.8N, the total weight of the petrol is 45 * 6.8 = 306N note that weight = mg so we no... more