1) A boy was running and collided with a post which he didn’t notice. His 70-kg body decelerated from 4.0 m/s to 0 m/s in 0.01 seconds.?
1) A boy was running straight at night when suddenly colliding with the a post which he didn’t notice. His 70-kg body decelerated from 4.0 m/s to 0 m/s in 0.01 seconds.
a. Determine the force acting upon his body.
b. Assuming same initial speed, if he had hit the bushes instead of the post, his momentum would have been reduced to zero in 0.18 seconds. Determine what the force on his body would have been for a cushioned collision.
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a) F = ma = m(v-u)/t = (70 kg)(4.0 m/s - 0 m/s)/(0.01 s) = 28,000 N
b) F = (70 kg)(4.0 m/s - 0 m/s)/(0.18 s) = 1556 N
From dP/dT = F, we have m dV/dT = F = 70*4/.01 = 28000 N. ANS. a
And similarly m dV/dT = F = 70*4/.18 = 1555.56 N. ANS b.