question_answer

                      Give reasons (i) It is difficult to balance our body, when we accidentally step on a peel of a banana. (ii) Pieces of bursting cracker fall in all possible directions. (iii) A glass pane of a window is shattered, when a flying pebble hits it. (iv) It is easier to stop a tennis ball than a cricket ball moving at the same speed. (v) A javelin thrower is marked foul, if an athlete crosses over the line marked for the throw. Athletes often fail to stop themselves before the line. (i) The reason is that one cannot exert action force effectively on the slippery peel of banana in the backward direction. Hence, in response the ground does not exert sufficient reaction the force in forward direction and hence we lose our balance. (ii) This can be explained on the law of conservation of momentum. When due to explosion some pieces move in the same particular direction, then in order to conserve momentum the remaining pieces move in the opposite direction. (iii) The reason is that, the glass pane of the window is a hard solid. The flying pebble suffers change in momentum in a very short time, so the force exerted by the glass window on the pebble will be large. Consequently the glass pane of the window will shatter. (iv) The reason is that mass of the cricket ball is more than that of a tennis ball. Thus, momentum is more in case of the cricket ball due to larger mass as compared to the tennis ball. So, less force has to be applied in the case of the tennis ball to stop. (v) The reason is that when athletes are running for the throw then due to inertia of motion they often fail to stop themselves before the line.                                                        (1x5)

Answer:

                    (i) frmto Thus, force is maximum in this period.     (1) (ii) a is negative fromto  (iii) From r=4sto?=8s,no force acts.         (1) (iv) y= 20 m/s from 4s to 8s.                        (1) (v) dfrom0to4s= 5m/s A from 4 to 8 s = 0 m/s2                (1)