# Help with Newtons laws and tension?

Help with Newtons laws and tension?

The block of mass M in the following figure slides on a frictionless surface.

Find an expression for the tension in the string.

Express your answer in terms of the variables m, M, and appropriate constants.

I tried starting with F=ma to get:

T=Ma <------ for block M

T=ma-mg <-- for Block m

But I can't figure out how to get a single expression out of them, and I can't see any other way to solve this. Can someone please help me?

selected by

Your 2nd equation is wrong: It should be

T+ma = mg

Substitute a on the equation of m from the equation for M.

You will get:

T=mg - m*T/M

=>T(1-m/M) = mg

=>T= mg/(1-m/M)

Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat. Duis aute irure dolor in reprehenderit in voluptate velit esse cillum dolore eu fugiat.

you did your algebra wrong. it is actually T= mg/(1+m/M)

Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat. Duis aute irure dolor in reprehenderit in voluptate velit esse cillum dolore eu fugiat.