# Help in 2 questions

1. Jan 4, 2010

### karin20061

A child of mass 24 kg stands at the center of a platform of radius 2.0 m and rotational inertia 740 kg·m2. The circular platform rotates about a frictionless shaft with an angular speed of 1 rad/s. The child walks along a radius until it reaches the rim. What is the angular speed of the platform when the child reaches the rim? [/I]

I found the answer for that..

the problem is: What is the difference in energy between the final and the initial energy of the child plus the platform? (Determine for yourself where the work that made this change comes from).

I tried kinetic energy, but it won't do.

2) The system in the Figure is in equilibrium. A mass M1 = 220.0 kg hangs from the end of a uniform strut which is held at an angle θ = 47.0° with respect to the horizontal. The cable supporting the strut is at angle α = 31.0° with respect to the horizontal. The strut has a mass of 52.0 kg. Find the magnitude of the tension T in the cable.
Find the magnitude of the horizontal component of the force exerted on the strut by the hinge?
Find the magnitude of the vertical component of the force exerted on the strut by the hinge?

I have no idea how to even start this question..:/

2. Jan 4, 2010

### JaWiB

For the first question: How much energy does the child gain? How much energy does the platform lose?

3. Jan 4, 2010

### jegues

For the second part you're going to have to draw us a free body diagram to show us what's going on.