Find mass of an object hanging on string

In summary, to find the mass of an object hanging on a string, use the formula α=(mB-mA/mB+mA) x g. This can be derived by using Fnet = ma for both masses A and B, and solving for the tension T, which can then be used to solve for the mass of object B.
  • #1
please tell me how to find the mass of an object which is hang on the string?
I mean what would be the formula ?
i am also writing here my numerical question...
Q:two bodies A and B are attached to a string which passes over a pulley so that two bodies hang vertically.if the mass of body A is 4.8 kg find the mass of body B which moves down with an acceleration of 0.2m/s.s.(g=9.8m/s.s)
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  • #2
Make a diagram of the situation.

Look carefully at mass B. How many forces act on mass B?
  • #3
no force is acting on mass B the formula given in our textbook is:
α=(mB-mA/mB+mA) x g

i don't know how to arrange it to find the mass B...:confused:
  • #4
We are trying to show HOW to get that formula.

Look at mass B. It has the Earth pulling it down - that is the weight mB x g of mass b - and the string pulling it up by a tension T.

Now use Fnet = ma for mass B.
  • #5
Fnet = ma ...for mass B

mBg - T = mBa

Fnet = ma ....for mass A

T - mAg = mAa

If the tension T is eliminated from the above two equations then one gets the equation required.

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