Question

Starting from rest, a 2.1x10-4 kg flea springs straight upward. While the flea is pushing off from the ground, the ground exerts an average upward force of 0.37 N on it. This force does 1.5x10-4 J of work on the flea. (a) What is the flea's speed when it leaves the ground? (b) How far upward does the flea move while it is pushing off? Ignore both air resistance and the flea's weight.

Answer 1

B)

W = Fd
(1.5 x 10^-4) = (0.37 - Fg)d
(1.5)(10^-4) = (0.37 - 9.8m)d
(1.5)(10^-4) = [0.37 - (9.8)(2.1)(10^-4)]d
0.00015 = 0.368d
d = 0.0004076 meters

A)

KE + PE = KE + PE
(1/2)mv^2 + (0) = (0) + mgh
(1/2)mv^2 = mgh
(1/2)v^2 = gh
v^2 = (2)(9.8)(0.0004076)
v = 0.08938 meters per second

Answer 2

where did you get 0.0004076