# Find mass of an object hanging on string

• angi-18
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.

#### angi-18

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)

Make a diagram of the situation.

Look carefully at mass B. How many forces act on mass B?

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...

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.

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.