# Angular Acceleration, Max/Min, and Grav. Attraction

1. Feb 24, 2008

### the7joker7

Here are three questions on my physics homework and my attempts to solve them...am I looking at this the right way?

Question 1: A tire placed on a balancing machine in a service station starts from rest and turns through 4.7 revolutions in 1.2 seconds before reaching it's final angular speed. Calculate its angular acceleration.

My attempt: Using formula x(t) = x$$_{0}$$+ v$$_{0}$$*T + (.5)at$$^{2}$$

I got

4.7 = .5(a)(1.2$$^{2}$$)

Solving for a, I got 6.522 rotations, or 40.98 radians.

Question 2: A car rounds a banked curve where the radius of curvature of the road is R, the banking angle is theta, and the coefficient of static friction is mu. Find the range of speeds the car can have without slipping up or down the road, and what is the range of speeds possible if R = 100m, theta = 10 degrees, and mu = 0.10?

The formula I pounded out was...

$$\sqrt{(((r*g(sin(\theta) - \mu(cos(\theta))))/(cos(\theta) + \mu(sin(\theta))}$$ < V < $$\sqrt{((r*g(sin(\theta) + \mu(cos(\theta))))/(cos(\theta) - \mu(sin(\theta)))}$$

I plugged in the numbers and wound up with 8.57 < V < 16.603, in any case, which I'm sure is right so long as my formula is right.

Question Three: Two schoolmate, Romeo and Juliet, catch each other's eye across a crowded dance floor at a school dance. Find the order of magnitude of the gravitational attraction that Juliet exerts on Romeo and vice versa. State quanities you take as data and the values you measure or estimate for them.

I basically just guessed my own masses (Romeo is 80kg and Juliet is 70kg) and the distance between is 12m. I used the formula

((m$$_{1}$$*m$$_{2}$$)/distance$$^{2}$$)*gravity to get 381.11N, of magnitude 10^2~.

That work?

Last edited: Feb 24, 2008
2. Feb 24, 2008

### Cyrus

Please post in the HW help section, and please revise you post using the text tool bar. I cant read what you wrote.

Its the equation editor in advanced mode.

3. Feb 24, 2008

### the7joker7

I'm not seeing the equation editor when I went to advanced mode...where is it?

4. Feb 24, 2008

### Cyrus

There is a small sigma symbol up top on the tool bar.

5. Feb 24, 2008

### the7joker7

Thanks! I've cleaned it up.