# 2 Physics Questions!

1. Nov 22, 2007

### staz13

Hey guys! I REALLY need some help with my physics. Here is one of my two questions:

1) With what rate of acceleration will a cart roll down a ramp inclined at an angle of 27 degrees? Assume the wheels of the cart are frictionless

I have NO idea how to even get started.

Here is the second one, 2) A coin is placed on a book that is slowly opened. It is noted that the coin does not start to move untill the opening angle is 25 degrees. What is the coeficient of friction between the book and the coin?

THANKYOU in advance if you can help at all!

2. Nov 22, 2007

### silently_loud

1.use F=ma for the first one. So mgxsinx27=ma, then gxsin27=a

2. Use f=un, so mgcos25=Normal.

Maybe use F-f=ma to find f then use f=un to find coefficient of friction

3. Nov 22, 2007

### staz13

For question 1 I got 4.45 m/s ^2. But i dont understand why you used mgsin27. How do we know thats the force? and not mgcos27

For question 2 i dont understand how you went from force of friction = unormalforce to mgcos25 . I also dont see how it helps because we dont have the mass.

4. Nov 22, 2007

### silently_loud

mgcos always equals the normal force. Unless its an object on the ground, which in that case w=n.

Alright. f=un. mgcosx25=n

f=uxmgcos25

mgxsin25=uxmgcos25

gxsin25=uxgcos25
g=9.8
solve for u