Physica question

Question

During the jump, the push-off force and gravity are important. The push-off force is the force of the ground on the volleyball player during the push-off.

We neglect air resistance in this exercise. The volleyball player has a mass of 75 kg. The push-off force is applied over the first 15 cm. After the first 15 cm its speed is 3.0 m/s.

16 4p Calculate the average pushing force over the first 15 cm.

17 3p Calculate the distance that the volleyball player still goes up after the push-off.

Answer 1

1) The 2nd Law for the player during the 15 cm. F_P - F_W = ma or F_P = m(g+a)

The upward acceleration, a, can be calculated from kinematics. Given v₀ = 0, d = .15 m, v = 3 m/s

2ad = v² - v₀² or a = v²/(2d)

solve for a, solve for F_P (note the importance of converting cm to m.

2) The second part is simply trying to find the height that a body goes given an intitial velocity. Here a = -g, v₀ = 3 m/s and v = 0 m/s (at y_max). Use the same kinematic equation, but solve for d = y_max

y_max = v₀²/(2g)

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