# Forces, magnitude and acceleration

1. Sep 27, 2004

### Angeluzmaia

Can someone help me please, with this problem???
I don't understand it

A 42.9 kg girl and a 54.8 kg boy are on the surface of a frozen lake, 15.0 m apart. Using a rope, the girl exerts a horizontal 4.35 N force on the boy, pulling him toward her. Calculate the magnitude of the girl's acceleration.

Thanxs a lot ...

Last edited: Sep 27, 2004
2. Sep 27, 2004

### vsage

Think about Newton's second law. They pair are initially at rest right? Considering this you know that the force the girl exerts on the rope to get the boy to come toward her is equal and opposite to the force the rope pulls back on her at because of the tension.

3. Sep 27, 2004

### Angeluzmaia

Can you help me with the formula?
I've been trying but I don't get it.

4. Sep 28, 2004

### vsage

mass of girl * acceleration of girl = -acceleration of boy * mass of boy

sum of the forces must equal 0 since they were initially at 0 acceleration as a system. (edit sorry it's like 3AM here I probably should have answered this sooner)