Question

An elevator plattom is going up at a speed of 20m/s and during the upward motion, a ball of mass
50 g falling in downward direction at a speed of
5m/s. The speed with which the ball rebounds after
an elastic collision with the platform is
(1) 25 ms'
(2) 5 ms-
(3) 45 ms'
(4) 35 ms-​

Answer 1

Answer:

45 ms'

Explanation:

e=v2-v1/u1-u2

u1=-5ms' (negative because ball is moving downward which we are taking as negative)

u2=v2=20ms'

e=1(perfectly elastic collision)

e×(u1-u2)=v2-v1

1×(-5-20)=20-v1

-25=20-v1

v1=20+25

hence, v1=45ms'.