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*22. A
40.0-kg boy, riding a 2.50-kg skateboard at a velocity of +5.30 m/s
across a level sidewalk, jumps forward to leap over a wall. Just after
leaving contact with the board, the boy’s velocity relative to the sidewalk
is 6.00 m/s, 9.50° above the
horizontal. Ignore any friction between the skateboard and the sidewalk. What
is the skateboard’s velocity relative to the sidewalk at this instant? Be
sure to include the correct algebraic sign with your answer. |
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Consider
the boy and the skateboard to be a single system. If we ignore the friction between the
skateboard and the sidewalk, then there is no external horizontal forces
acting and the momentum in the x direction must be
conserved. Note, since the boy
is airborne and the skateboard cannot go through the sidewalk, there must be
some force in the y direction and so the y momentum is not conserved in this
case. |
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Minus sign indicates that
skateboard moving opposite direction as the boy! |
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