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AirForceOne
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Homework Statement
A small block of mass m rests on the sloping side of a triangular block of mass M which itself rests on a horizontal table. Assuming all surfaces are frictionless, determine the magnitude of the force F that must be applid to M so that m remains in a fixed position relative to M (that is, m doesn't move on the incline).
Homework Equations
F = ma
The Attempt at a Solution
I find the forces on block m due to gravity and the force F. So the net force on that block is:
Fcos(theta)+mgsin(theta)=ma
Since the block m isn't moving, I set the net force on it equal to zero (?):
Fcos(theta)+mgsin(theta)=0
And I solve for F:
F= -mgtan(theta)
The actual answer is:
F=(m+M)gtan(theta)
What am I missing? I've been scratching my head for awhile now...