Question

A particle of small mass 'm' is joined to a very heavy body 'M' by a light string passing over a lift pulley. Both bodies are free to move. The total downward force on the PULLEY is nearly :

1)mg
2)2mg
3) 3mg
4)4mg
5)Can't be determined.

Answer 1

Consider the attachment below:

Now,

Ma = Mg - T                    (equation 1)

Ma= T - Mg                     (equation 2)

Diving (equation 1) by (equation 2) we get

M/m=Mg-T/T-Mg

Or,

T=2mMg/M-m

Since

M > > m

M-m=M

Thus,

T=2mg

Now,

net downward force on the pulley=2T=4mg

Thus the correct option is (4)