Tiêu đề Notes_Short Answers_04.Forces.pdf ✅

1. The apparent weight of an object increases in an elevator while accelerating upward. A moongphaliwala sells his moongphali using a beam balance in an elevator. Will he gain more if the elevator is accelerating up? Ans:No [Sol. Effect will be on both side.] 2. A boy puts a heavy box of mass M on his head and jumps down from the top of a multi-storeyed building to the ground. How much is the force exerted by the box on his head during his free fall? Does the force greatly increase during the period he balances himself after striking the ground? Ans: Zero, Yes [Sol. (a) Zero, as both fall down with acceleration g downward. In the reference frame of body. N + mg = mg N = 0. (b) When they reaches on ground both will have velocity and as the block is stopped in small time force is exerted by man in form of normal which is large as time is small. ] 3. A person drops a coin. Describe the path of the coin as seen by the person ifhe is in (a) a car moving at constant velocity and (b) in a freely falling elevator. Ans: (a) moves down (b) coin stays with him. [Sol. If car is moving with velocity v both man and coin will have velocity v in horizontal. So, coin will be in rest w.r.t. man in horizontal all the time but will gain vertical downward velocity so its path will be vertical downward. ] mg N mg Upward mg is pseudo force v N o v  v  v  g g  o Force And Motion g g