Question

A 5-kg rock is on the ground and a girl lifts up on the block with a force of 32 N. The NORMAL force exerted by the ground on the rock would be approximately

a)18 N down
b)82 N up
c)82 N down
d)32 N up
e)18 N up

I think the normal force would be upward because it's perpendicular to the surface, so would it be 18 N up? I'm not really sure what I'm doing.

Answer 1

The weight minus 32 N upward
So what is the weight?
weight = m g = 5 * 9.81 call it 50
50 - 32= 18 N upward sure enough

Answer 2

If it were not upward the rock would accelerate down through the ground toward the center of the earth :)