Explanation
Distance = 20 + [20 – (-20)] = 60 m.
Displacement = -20 – 0 = -20 m.
If v1 and v2 are the velocity of two bodies, then in the first case, the relative velocity is v1 + v2 = 8.
In the second case, the relative velocity is v1 - v2 = 2.
On solving, v1 =5 m/s and v2 = 3 m/s.
Relative speed = 0 when vel. Of A = vel. Of B
∴ displacement – time graphs of A and B must have same slope (other than zero).
Here ball and belt are moving in the same direction. So speed of ball w.r.t. observer on stationary platform = 9 + 4 = 13 ms-1 from A to B.
(A) Check by dimensions
To stop the train, force is being applied on the train in the backward direction. Due to inertia of motion, the apple falls slightly away from the hand in the direction of motion ofthe train.
At B, slope of v – t curve is negative i.e. velocity decreases with time. Hence there is a forcewhich opposes the motion.
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