# Homework Help: Block moving around in a semi cricle

1. May 3, 2012

### arrax

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

A cylinder is cut out of a large block with mass M=4kg sitting on a table. A small block of negligible size and mass m=0.5kg is placed within the hole. All the surfaces are frictionless. The radius of the cut is R=0.80m and the angle is 25 degrees.

Basically there's a block with a semi-circle cut into it. Inside the semi circle is a block that is positioned 25 degrees to the left from bottom dead center. And there is a force F pushing this big block with a semi-circle cut to the right. So when you push the block, the little block in the half pipe moves. I'm supposed to find the FORCE on the big block that makes the small block move 25 degrees and the force of the block on the mass m (the small block)

2. Relevant equations

F=ma, Circumference = 2∏r

3. The attempt at a solution

i have no idea where to start, but for the small block i tried using tanθ = a/g, but I came out with 4.575 m/s^2 for my a which seems way too fast.

2. May 3, 2012

### tms

Start where one should always start: by writing down the forces acting on the blocks (separately). There are two on the small block: one is gravity and the other is ...

3. May 3, 2012

### arrax

The other is the M block acting on the small block, and So gravity does act on the small block so I do end up using tan25 deg = a/g I think because of the force of the big block acting on the small block on the x axis.

4. May 3, 2012

### tms

Recall that the small block is very small. The force of the big block on the small will be the same as the force of an inclined plane tangent to the hole would be.