Difference between applied tension and tension due to weight?

AI Thread Summary
The discussion centers on understanding the difference between applied tension and tension due to weight in a physics problem involving a block on a table and a hanging mass. In Case I, a 50 N force is applied directly to the string, resulting in a tension of 50 N. In Case II, a 5 kg block is attached, leading to a calculated tension of 40 N due to the presence of additional mass and friction. The equations reveal that the acceleration is lower in Case II because the system's net force is reduced by the weight of the block and frictional forces. This illustrates how the dynamics of the system affect the tension in the string.
Petrikovski
im trying to do this AP problem that involves a block on a table attached to a string which hangs over a pulley. in Case I 50 N is applied to the string and in Case II a 5 kg block is attached. the tension in Case I is 50, but according to my packet in case II the tension in Case II is 40. why would 50 N applied directly be more tension than Fw = 5x10 = 50 N?
 
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btw the block on top is 10kg and there is a coefficient of friction of .2
 
Because in the second case there is more mass so there's less acceleration:
mg - Fs = (M+m)a
50 - 20 = 15a
a = 2
Now looking at the 5kg weight:
50 - T = 5a
T = 50 - 10 = 40
 

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