# Homework Help: Friction and Moving Blocks

1. Feb 3, 2010

1. The problem statement, all variables and given/known data
A block of mass m1 = 280 g is at rest on a plane that makes an angle θ = 30° above the horizontal. The coefficient of kinetic friction between the block and the plane is μk = 0.10. The block is attached to a second block of mass m2 = 220 g that hangs freely by a string that passes over a frictionless and massless pulley. Find its speed when the second block has fallen 30.0 cm.
cm/s

2. The attempt at a solution

Mass 1 Mass 2
Fground=280*9.81=2746.8 N Fm2 ground=220*9.81=2158.2 N
Fgy=Fgcos(30)
=433.714 N
Fgx=Fgsin(30)
=250.405 N
Fkinetics=(.1)*(250.405)
=25.04 N
Fx= 250.405-25.04= 225.36N

Fx=max
225.36=280*ax
ax=.805 m/s2

Thank you!

2. Feb 3, 2010

### songoku

friction = normal force x coefficient of friction, and the normal force is not equal to the force on x-direction.

There are total 3 forces on the x-direction. You are one less

3. Feb 3, 2010

So in the x direction I have...

For the second mass the Fg=2158.2N

and on the first mass Fgx=250.405 N
and friction which= 433.714*.1=43.37 N

Would it be:

2158.2+250.405-43.7=max

2364.905=280ax

or is "m" both of the masses and acceleration is squared?

4. Feb 4, 2010