# Me with this phy problem, thx

1. Sep 27, 2004

### 1stcool

plz help me with this phy problem, thx

In Figure 5-39, a crate of mass m = 210 kg is pushed at constant speed up the frictionless ramp ( = 26.0°) by a horizontal force F.

http://www.webassign.net/hrw/hrw7_5-39.gif

What is the magnitude of the force exerted by the ramp on the crate?

I use m*g to find Fg, and then using Fg*cos⊙(26) to find Fn(normal Force) but I got it wrong, can anybody help me, thx.

2. Sep 27, 2004

### Staff: Mentor

The normal force would be $mg cos\theta$ only if there were no horizontal force F. Instead, consider all the forces acting on the crate (I see three) and apply the conditions for equilibrium.

3. Sep 27, 2004

### 1stcool

three? is it Fg, F and Fn?

4. Sep 27, 2004

### Staff: Mentor

That's correct.

5. Sep 27, 2004

### 1stcool

ok, thx Doc Al