# Physics

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What is the acceleration of the upper block? The coefficient of kinetic friction between the lower block and upper block is 0.0005. The coefficient of kinetic friction between lower block and floor is 0.0001. Upper block is 1kg, lower block is 2kg, and Force of 20N is applied to lower block.
Here's a picture:

img217.imageshack.us/img217/3526/2505100050.jpg

I got 20 m/s as the acceleration of the upper block. Is this right?

• Physics -

Sorry here's the picture:

img245.imageshack.us/img245/3526/2505100050.jpg

• Physics -

No; it's not right. First of all, 20 m/s is a speed, not an acceleration.

The two masses accelerate at different rates because there is very little friction and the top mass tends to be left behind. The top mass (#2) is accelerated only by the kinetic friction force between the blocks, which is
0.0005 M2 g = M2*a2, so
a2 = 0.0005 g = .0049 m/s^2
and the force that accelerates M2 is just M2 a2 = 0.0049 N

The force that accelerates M1 is
20N - (3 kg)(0.0001)g - 0.0049 = M1*a1
20N - .0029N - .0049N = 2 a1
a1 = 9.996 m/s^2

• Physics -

Thank you! I see where I went wrong