question_answer

A block of mass M is pulled along a horizontal frictionless surface by a rope of mass m. If a force P is applied at the free end of the rope, the force exerted by the rope on the block is

A) \[\frac{Pm}{M+m}\]                      

B) \[\frac{Pm}{M-m}\]

C)  P                                           

D) \[\frac{PM}{M+m}\]

Correct Answer: D

Solution :

Let acceleration of system (rope + block) is a along the direction of applied force. Then, \[a=\frac{P}{M+m}\]Draw the FBD of block and rope as shown in figure. where, T is the required parameter. For block     T=Ma \[\Rightarrow \]\[T=\frac{MP}{M+m}\]