Dan is gliding on his skateboard at 2.56 m/s . He suddenly jumps backward off th

Question

Dan is gliding on his skateboard at 2.56 m/s . He suddenly jumps backward off the skateboard, kicking the skateboard forward at 8.02 m/s (as measured by an observer on the ground). Dan's mass is 68.1 kg and the skateboard's mass is 5.99 kg .

A) How fast is Dan going as his feet hit the ground? (I already got this answer 2.08 m/s)

B) If the jump requires 0.112 s to complete, what average force did Dan exert on the skateboard?

Include the direction of the force as an appropriate positive or negative value assuming that Dan was moving in the positive (forward) direction initially.

Explanation / Answer

from the impulse momentum theorem the cange in momentum of Dan is impulse

Impuse = change in momentum of dan

Ft = m(dan) ( vf-vi)

F = m(dan) ( vf-vi)/t

= 68.1 kg ( 2.08- 2.56)/ 0.112

=-291.85 N

negtave sign indicates force along toward left side ( backward) side

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