Physics - NLM Question with Solution | TestHub
Figure shows two identical blocks of mass m kept on a smooth floor. Block A is connected to front wall with a just straight string and block B is connected to rear wall with a relaxed spring Assume that the floor of the train car is smooth and exerts no horizontal forces on the block. Mark the correct statement(s). Initially train is moving with constant speed.
Options:(select one or more)
Answer:
Solution:
Analyse in the ground frame; the train's acceleration a creates pseudo forces in the train frame.
(A) Constant velocity means a = 0: no pseudo force, the string stays just straight and the spring relaxed - no force in either. Correct.
(B) Train speeds up: pseudo force pushes both blocks backwards. The string tied to the front wall becomes taut and pulls A forward; the spring tied to the rear wall gets compressed and pushes B forward. But the string tension adjusts instantly while the spring force builds only as the compression develops, so the forces exerted on the two blocks are not the same. So the statement is wrong.
(C) Train slows down: pseudo force acts forward, pushing block A towards the front wall. Correct.
(D) While slowing down, the string is slack and the floor is smooth, so no horizontal force acts on A; in the ground frame A simply continues with its earlier constant velocity - resultant force on A is zero. Statement wrong.
Hence correct statements are (A) and (C).
