# Help:Equilibrium & Angular Momentum

1. Nov 11, 2004

### buffgilville

1) A plank of mass 2.5 kg and length 2 meters is resting horizontally on two wedges. The first is at one of the ends and the other is a distance 0.3 meters from the second end. If a mass of 0.2 kg is placed on this second edge, what is the force (in Newtons) acting on the second wedge.

Here's what I did:
T1=F1(0) = 0
T2=F2(1.7)
T(mass)=-(0.2*9.81*2) = -3.924
T(plank)=-(2.5*9.81*(2/2)) = -24.525
sum of torque = F1(0) + F2(1.7) - 3.924 - 24.525 = 0
so, F2=16.73 Newtons
but the correct answer is 1.71 Newtons. Where did I go wrong?

2) The mass of the earth is 6.0E24 kg and its radius is 3950 miles. Assuming that the earth is a uniform sphere, its angular momentum (in Joule. Secs) is aE+33 where a is?

I = (2/5) MR^2 ---> (2/5)(6.0E24)(6355550meters)^2 = 9.694E37

L = Iw ---> (9.694E37)((2pi)/86400) = 7.0499E33
which makes a=7.050

Last edited: Nov 11, 2004
2. Nov 12, 2004

### buffgilville

Is there anyone that can help me with these two problems?

3. Nov 12, 2004

### CartoonKid

All your workings looks fine. I don't know why you couldn't get the answer. Are you sure you were looking at the correct answer?

4. Nov 12, 2004

### buffgilville

I'm sure the answers that I got were wrong because I worked out other similar problems (same problem but with different numbers) with the same method and still got it wrong.

5. Nov 12, 2004