Physics education research, electronic materials, and the musings of Christopher Moore, Ph.D.

As you are biking, you run over a 17 g pebble and it gets stuck in your tire with radius 91 cm. You are biking at 12 m/s. After it travels around the tire a few times, the rock is flung from the tire as it is on top of it. How fast is the pebble traveling as it leaves your tire?

So I'm thinking I use p=mv, since they give me mass (1700 kg) and velocity (12 m/s). But then velocity of the pebble..how would I find that?



The moment of inertia of a mass moving around a point is just the object’s mass times the square of the radius (mr^2). What would be the equation for the moment of inertia of two objects moving around the same point?

Since it's two objects, would it be 2mr^2?



Spinning objects can experience friction just like non spinning objects. If you have a disk of mass 304 g with a radius of 164 mm, what is its acceleration if you apply a force of 14 N at the edge and friction applies a force of 14 N on the axle, 12 mm from the center?

I know I use I = 1/2mr^2 to get 408.8 kgm^2. But then how would I use the 14 N and 12 mm?



You are now spinning a rock on the same string at an angle above your head. You want the rock to hit an object at the peak of its flight, 7 m up and 12 m away. If you will launch it at 30°, how fast should be spinning it in rad/s?

This one I just have no clue on. I don't even know how to start it.


By the way if you help me on these, i will do my best to help you on any problems you might have.