Newton's Second Law: Combined Masses

[Peter G.]

A block sits on a horizontal frictionless table. A thread attached to its runs horizontally to a pulley at the edge of the table, passes over the pulley and supports a load of 1.0 kg. The size of the acceleration of both the block and the load is 2.0 m/s.

Find the tension in the thread:

To answer this, I used the load:

Acceleration was downward so weight must be greater than tension, thus:

W - T = ma
10 - T = 1 x 2
10 - 2 = T
T = 8

Now use the Free Body force diagram for the block to find the mass of the block:

F = ma
T = ma
8 = 2m
m = 4.0 kg

I'm not sure if my methods are correct, anyone can help me please?

Thanks,
Peter G.

 

[PhanthomJay]

Your methods are very good. But since you rounded off g to 10 m/s^2, the mass of the block on the table should be 4 kg, not 4.0 kg. If you used g = 9.8 m/s^2, then m = 3.9 kg.

 

[Peter G.]

Ah ok, thanks a lot PhanthomJay.