Question

Batman (m = 85 kg) is trying to rescue Robin (m = 50. kg), who has fallen over the side of a building. Robin is hanging from the Batcable® while Batman is on the roof holding the other end and sliding perilously close to the edge. If the coefficient of friction between Batman and the roof is 0.25, what is their acceleration?

Answer 1

Forces acting on Batman and Robin:

$$Ma=T-\mu Mg,\\ -ma=-mg+T.$$

The solution of the system gives us the answer:

$$a=2.09\text{ m/s}^2,\\ T=386\text{ N}.$$