Question

A ball of mass $1kg$ strikes a heavy platform, elastically, moving upwards with a velocity of $5m/s$.The speed of the ball just before the collision is $10m/s$ downwards. Then the impulse imparted by the Platform on the ball is (e=1) :-

• A. $15N-s$
• B. $10N-s$
• C. $20N-s$
• D. $30N-s$

Answer 1

The correct option is D $30N-s$

The speed of the ball in the reference frame of the plank is given as,

$v=10+5$

$v=15m/s$

The change in momentum of the ball is the impulse and it is given as,

$mv=15+15$

$=30N\cdot s$

Thus, the impulse is $30N\cdot s$.