- #1
Dansuer
- 81
- 1
Homework Statement
http://img823.imageshack.us/img823/5238/immaginelq.th.jpg
Uploaded with ImageShack.us
What horizontal force [itex]F[/itex] must be constantly applied to [itex]M[/itex] so that [itex]M_1[/itex] and [itex]M_2[/itex] do not move relative to [itex]M[/itex]? neglet friction
Homework Equations
The Attempt at a Solution
Since [itex]M_2[/itex] is not moving, the tension of the string is [itex]T=M_2 * g[/itex]. Plugging this into the euation [itex]T=M_1 * a[/itex] we find
that the acceleration of [itex]M_1[/itex] is [itex]a=(M_2 / M_1)*g[/itex]
Since [itex]M_1[/itex] is at rest with respect to [itex]M[/itex], [itex]M[/itex] have the same accelleration [itex]a[/itex]
So, [itex]F = (M + M_2) * a[/itex]. or [itex]F = (M_2 / M_1)*(M+M_2)*g[/itex]that's what i found. But the problem solution states that [itex]F = (M_2 / M_1)*(M+M_1+M_2)*g[/itex]
which i don't see why it should be like that. Intuitively if i push on the block [itex]M[/itex], i push both [itex]M[/itex] and [itex]M_2[/itex], that's why i
found [itex](M+M_2)[/itex], but i don't push on [itex]M_1[/itex], since there is no friction. It's movements are due to the force of [itex]M_2[/itex]
pulling down.
Last edited by a moderator: