1) A .65 kg on the end of thin light rod is rotated in a horizontial circle of a radius 1.2 m. (a) Calculate the moment of inertia of the ball about the center of the circle, and (b) the torgue needed to keep the ball rotating at constant angular velocity if air resistence exerts a force of .020 N on the ball. (ignore rod's moment of I and air resistence).(adsbygoogle = window.adsbygoogle || []).push({});

So... I did find (a) successfully: I = mr^2 = .94 kg-m^2

And here were my thoughs for part (b): T = F(perpindic)r

T = I*a(angular) Since acceleration is constant is it not zero?correct answer: .0240 mN

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2)To get a flat uniform cylindrical satellite spinning at the correct rate, engineers fire four tangential rockets. If the satellite has a mass of 3600 kg and a radius of 4 m, what is the require steady force of each rockets if the satellite is to reach 32 rpm in 5 minutes?

This one really got me thinking. So first converted all I needed to. I was give:

m = 3600 kg, r = 4 m, w = 3.349 rads/2, = 300 s.

I know I have to use the F = ma, and I have the m so all I need to do is some how get the a, and that is where I am having trouble.Correct answer: 20 N

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3) A bowling ball of mass 7.3 kg and radius 9 cm = .09 m, rolls without slipping down a lane at 3.3 m/s. Calculate it's total kinetic energy.

What I did was use the equation: (1/2)Iw^2

First I found I by I=mr^2

I = .059

then I found w by w = v/r = 3.3/.09

w = 36.6

so .5(.059)(36.6^2)

= 39.5 J and the correct answer is56 JWhat did I do wrong?

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# Homework Help: Some problems with rotational motion

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