Posted by John on .
A 33.4 kg child, with a 3.05 kg backpack on his back, first stands on a sidewalk and then jumps up into the air. Find the force (positive up/negative down) on the sidewalk from the child when the child is (a) standing still and (b) in the air. Now find the net force (positive up/negative down) on Earth due to the child when the child is (c) standing still and (d) in the air.

Physics 
Damon,
m = 33.4 kg +3.05kg = 36.45
Fup on child = 36.45*9.81 = 358 Newtons
so
a) Fdown on sidewalk = 358 Newtons
b) zero
c) 358 Newtons
d)zero