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View Full Version : plz help me with this phy problem, thx

1stcool
Sep27-04, 08:15 PM
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.
Doc Al
Sep27-04, 08:34 PM
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.
1stcool
Sep27-04, 08:52 PM
three? is it Fg, F and Fn?
Doc Al
Sep27-04, 09:06 PM
three? is it Fg, F and Fn?
That's correct.
1stcool
Sep27-04, 09:08 PM
That's correct.
ok, thx Doc Al