A 36kg child is moving on a 20kg skateboard at speed 60 ms w

A 36-kg child is moving on a 2.0-kg skateboard at speed 6.0 m/s when she comes to a ledge that is 1.2 m above the surface below. Just before reaching the ledge, she pushes off the board. The board leaves the ledge moving horizontally and lands 8.0 m horizontally from the edge of the ledge. Make a list of the physical quantities describing the motion of the child after leaving the ledge and determine two of them. Describe any assumptions you made.

Solution

t = sqrt ( 2 h / g)

= sqrt (2 * 1.2 / 9.8) = 0.495 s

launch speed v = d / t

= 8.0 / 0.495 = 16.17 m/s

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From conserve momentum p_initial = p_final

(36 + 2.0) * 6.0 = 36 * V + 2.0 * 16.17

speed of the child after leaving the ledge V = 5.44 m/s

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kinetic energy of the child after leaving the ledge

KE = 1/2 m v² = 0.5 * 36 * 5.44²

= 532 J