1. The problem statement, all variables and given/known data Consider a mechanical car jack. To change a wheel it may need to lift a load of 2000N. Suppose that one rotation of the screw raises the car by 10mm. You apply a force to the end of the lever, 0.5m long, through a full circle. The jack is only 40% efficient. Calculate the force that you have to apply. (This is a textbook question from OCR, AS Physics.) 2. Relevant equations probably to do with moments: anti-clockwise moments = clockwise moments work done: work done = force x perpendicular distance... GPE: gravitational pe = mass x g x height I don't know where to begin, etc.. 3. The attempt at a solution There is answer at the back of the textbook, but I won't show it for now, so that it doesn't affect your way of workings, or anything... I'll show it if needed though. Thank you for any help!