# Newton's Laws of Motion : Block Problem

1. Jan 10, 2014

### rajumahtora

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

In the arrangement shown, all surfaces are frictionless, mass of block M = 30 kg and m = 20 kg.
If F = 180 N , Find accelerations of both the blocks

2. Doubt

What amt of force will act on larger block M, just T(coz of horizontal string around the pulley) or 2T(coz of both the strings around the pulley)

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2. Jan 10, 2014

### Jilang

Imagine that the pulleys were not attached to anything else except the string. In which directions do you think they would be pulled?

3. Jan 10, 2014

### tiny-tim

hi rajumahtora!

when you consider the forces on a body, you must consider the whole body …

the block M is attached to the pulleys, so you must consider the external forces on the block-plus-pulleys

4. Jan 11, 2014

### tiny-tim

(please don't start a new thread)

as i said before, so you must consider the external forces on the block-plus-pulleys (as a single body), not just the block on its own

5. Jan 11, 2014

### haruspex

rajumahtora, please clarify your question. There are two pulleys attached to M. Are you asking what the net force on M is from the two pulleys, or what force each pulley exerts on the block separately?
(What do you think the two separate forces are?)

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