Question

Why is tension added?

Why is my teacher saying that T = mg + ma = 24 N?

Shouldn't it simply be 4 N?

Link to the question
https://ibb.co/dHiDkk

Answer 1

Yes, the tension T is 24N. The work done by the tension is 96J.

Explanation:

Since the net force will cause an acceleration of `2 ms^-2`, `F_(NET) = 2*2 = 4N`.

Given that the tension should act upwards opposite to the direction of the gravitational force (downwards), both forces cancel each other out to give a net force of 4N.

A tension of 24N upwards subtract by downwards gravitational force of 20N will give a net force of 4N upwards.

Work done of a force is the product of the applied force and the distance moved in the direction of the force.

Using kinematics to find the distance moved:
`s=ut+1/2 at^2= 1/2(2)(2)^2 = 4m`

Thus, work done `W= Fd = (24)(4)= 96J`.