Newton's Laws of Motion : Block Problem

[rajumahtora]

Homework Statement

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)

 

[Jilang]

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

 

[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

 

[tiny-tim]

Homework Statement

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

How much force will be applied on the larger block M by the pulley(coz of tension)?
1. T towards right
2. T towards up
3. T√2 45° to the right
4. Any other answer


3.Reason for doubt

If the total for exerted on the T i(cap) + T j(cap) i.e. Fnet on Bock M due to tension of string on pulley is T√2,
then there will be a force which will tend to pull block M upward...and if the accln of string is much higher, then the tension in the string will cause the block to accelerate up.

[To Jilang and tiny-tim,
After reading ur answer, i had this doubt too...so i asked again]

If anything else, please answer...
Thanks

(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

 

[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?)