A car of mass is initially at rest on the boat of mass tied to the wall of dock through a massless, inextensible string. The car accelerates from rest to velocity in times . At the car applies brake and comes to rest relative to the boat in negligible time. Neglect friction between the boat and water; the time at which boat will strike the wall is
a) 

b) 

c) 

d) 
None of these 
A car of mass is initially at rest on the boat of mass tied to the wall of dock through a massless, inextensible string. The car accelerates from rest to velocity in times . At the car applies brake and comes to rest relative to the boat in negligible time. Neglect friction between the boat and water; the time at which boat will strike the wall is
a) 

b) 

c) 

d) 
None of these 
(b) Till time friction on car will be in forward direction and on boat in backward direction. So the boat will not move till . Let be the velocity of car +boat system just after applying the brakes. From conservation of momentum, Time taken is 