# Homework Help: Acceleration and Force

1. Oct 20, 2008

### halo9909

1. The problem statement, all variables and given/known data

A 50-kg crate is pulled across the ice with a rope. A force of 80 N is applied at an angle of 36° with the horizontal. Neglecting friction, calculate

(a) the acceleration of the crate.
m/s2
(b) the upward force the ice exerts on the crate as it is pulled.

2. Relevant equations

F=Ma
law of Cosines
law of sines

3. The attempt at a solution

I have the upward force "Fay" which is 443N
using the law of sines 80sin36 = 443N which is the vertical force and usig the law of cosines the horizontal is 64.72N

I am not sure how to calculate the acceleration

2. Oct 20, 2008

### hage567

Use F=ma. What is the force acting on the crate in the horizontal direction? That is the force that is causing the crate to accelerate.

3. Oct 20, 2008

### halo9909

oh wow thanks
so you use the "horizontal" force and with F=ma
the horizontal force of 64.72=50kg *a
it becomes 1.2944m/s

So you would always use the horizontal force to the ground for accleration or only in this case?

4. Oct 20, 2008

### hage567

Since the crate is only moving in the horizontal direction (so it isn't rising falling - it stays in constant contact with the ice) the acceleration is only in the horizontal direction. I wouldn't say you always use the horizontal force, it depends on the situation.