# physics

posted by
**Anonymous** on
.

A boy weighing 4.2 102 N jumps from a height of 1.80 m to the ground below. Assume that the force of the ground on his feet is constant.

(a) Compute the force of the ground on his feet if he jumps stiff-legged, the ground compresses 2.20 cm, and the compression of tissue and bones is negligible.

(b) Compute the force his legs exert on his upper body (trunk, arms, and head), which weighs 2.50 102 N, under the conditions assumed above.

(c) Now suppose that his knees bend on impact, so that his trunk moves downward 44.0 cm during deceleration. Compute the force his legs exert on his upper body.