# Homework Help: Friction problem of a block

1. Nov 17, 2008

### nns91

1. The problem statement, all variables and given/known data

1.Lou bets an innocent stranger that he can place a 2kg block against the side of a cart, and that the block will not fall to the ground, even though Low will use no hooks, ropes, fasteners, magnets, glue, or adhensives of any kind. When the stranger accepts the bet, Lou begins to push the car to the right. The cooefficient of static friction between the block and the cart is 0.6.

Find the force of the friction on the block if a=32.27 m/s2 (It is double the minimum acceleration for the block will not fall to the ground).

2. A simple Atwood's machine uses two masses, m1 and m2. Starting from rest, the speed of the two masses is 4 m/s at the end of 3.0s. At that instant, the kinetic energy of the system is 80 J and each mass has moved a distance of 6m. Determine values of m1 and m2

2. Relevant equations

Fs= coeff * Fn[/SUB

U=mgy.

3. The attempt at a solution

1.So I found the normal force and time by the coeff of friction. how wever I got 130 N which is the wrong answer. What did I do wrong here ??

2. So I did the U for m1 and m2 and get.

U1=m1g*6
U2=m2g*-6

Then I add 2 equations together and get m1-m2= 80/6g

I know that I need one more equation since I have 2 unknowns but I cannot think of what I can do with the speed and time info. Can anyone help me ?

Last edited: Nov 17, 2008
2. Nov 17, 2008

### nns91

Does acceleration play any part in number 2 ??

3. Nov 18, 2008

### nns91

Has anyone found out anything yet ?

I was still stuck at figuring out the 2nd equation relating to the given speed and time.