# Q in dynamics, kinetics, Energy

1. Nov 20, 2009

### vemplord

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

1 Kg block slides on a circular rod (no friction) from rest in A position by a force of 40N. What is the speed when it reached point B. (see attached pic)

2. Relevant equations

W(f)=E(B)-E(A)

3. The attempt at a solution
The energy in A is 0, the energy in B is mgh+0.5mv^2
My problem is how to find the work of the force.

Thx.

#### Attached Files:

• ###### 1B.JPG
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2. Nov 20, 2009

### tiny-tim

Welcome to PF!

Hi vemplord! Welcome to PF!

(try using the X2 tag just above the Reply box )
Work done = force "dot" displacement …

so for a small angle dθ, find the displacement, "dot" it with the force, and then integrate.

3. Nov 21, 2009

### vemplord

Thanks,

I tried that:
The Y displacement is rsinθ an X displacement is r-rcosθ, tried to integrate from "0" to "π/2" but it doesn't come out right.

What am i doing wrong?

4. Nov 21, 2009

### tiny-tim

dunno show us!