1.

A glass marble whose mass is 100gm falls from a height of 40m and rebounds to a height of 10m. find the impulse and the average force between the marble and the floar. If the time during which they are in contact 0.2 sec

Answer»

M = 100 gm
h = 40 m
velocity before TOUCHING the FLOOR = u  m/s
   u² = 2 g h =  2 * 9.8m/s² * 40 m= 784
   u = - 28 m/s   downwards.

height of rebound = 10 m
velocity after touching the ground = v  m/s
 v² = 2 g h = 2* 9.8 * 10 = 196 
 v = 14 m/s

Impulse is equal to the change in linear momentum during the impact/collision
     = m v - m u  = 100 /1000 kg * (14 - (-28)) = 4.2 kg-m/s  or N-sec

AVerage force during the impact = 4.2 N-sec/0.2 sec = 21 Newtons.


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