I need some physics help!!

Question

Hi, I needed some help regarding some physics problems:

1. A 50kg girl pulls a 20 Kg wagon with a force of 10 N. The wagon accelerates at 2 m/s2. What is the force, in Newtons, exerted BY the wagon ON the girl?

2. A small girl applies a horizontal force of 2 Newtons to a 10 Newton box which slides across the floor with a constant speed of 3 m/s. What is the FRICTIONAL FORCE, in Newtons by the floor on the box?

3. A 600 N force is applied to a safe full of gold which weighs 2000N's but it does not move. What is the friction force exerted by the floor to the safe?

Any help would be greatly appreciated. Thank you!

Answer 1

(1) From Newton's Third Law, 10 N.

Yes, I know, it seems like the force applied BY the girl ON the wagon should be greater than the force BY the wagon ON the girl. But it just ain't so.

(2) 2 N.

The box is moving at constant horizontal velocity, so the net horizontal force on the box is zero.

(3) 600 N.

Again, the safe is in equilibrium. The net horizontal on the safe is zero.