Arock climber uses a pulley system to pull himself 10 m up a tricky part of a rock face. if the pulley system has a mechanical advantage of 3 and the climber weighs 786 n, what force does he use?

Mechanical advantage M is the ratio of output force Fo and the input force Fi and it tells us how much times does a machine multiply the input force. In our case M=3 and Fo= 786N because we need the machine to output the same force as the climbers weight to pull him up. Lets input the numbers: 

M=Fo/Fi

Fi=Fo/M=763 N/3=262 N.

So we want to input 262 N of force to get 763 N of output force.