Question

1. A 55.0 kg pole vaulter running at 11.0 m/s vaults over the bar. Assuming that the vaulter's horizontal component of velocity over the bar is 1.0 m/s and disregarding air resistance, how high was the jump (include units)?


2. A 71 kg person rolls on a 2 kg skateboard with a velocity of 6 m/s. The skateboarder runs into a large rubber band with a spring constant of 80 N/m. How far will the cord stretch till the skateboarder stops moving forward (include units)?

Answer 1

kinetic energy coming to the jump = (1/2) m(121)
kinetic energy at the top = (1/2) m (1)

loss of Ke = (1/2) m (120)
= gain of potential = m g h

(note that the mass is irrelevant, big person goes as high as small one if same speeds)
so
(1/2)(120) = 9.81 h
solve for h

Answer 2

ke = (1/2) m v^2
goes until that energy is stored in spring
so
(1/2) m v^2 = (1/2) k x^2