# How do i calculate the tension in string here? [closed]

How do I calculate the tension of string? I have already calculated the acceleration of the 2 masses which is 3m/s. But I can't seem to arrive at the answer which is 9.00N. Sorry if this was a straightforward question.

• Do a free body diagram on the 3kg block - what force would be required to accelerate a 3kg block at the acceleration you calculated? May 2 at 3:48
• It would be 9N, is that the tension? May 2 at 3:51

As you correctly found acceleration of the centre of mass, and hence of both the blocks (as both must be moving with same acceleration to keep the string taught) is $$3m/s^2$$. Now draw a free body on 3kg mass, it is moving with $$3m/s^2$$ acceleration with only force acting on it i.e tension. So tension = 3*3=9N