Question

as shown in the figure a man pushes compartment accelerating uniformly towards left. if the man stays at rest relatively to the compartment, which of the following is correct.
a. the man does positive work on compartment
b. the man does negative work on compartment
c. the man does 0 work on the compartment.

please explain the answer
(given answer: b)

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Answer 1

Here, b. the man does negative work on compartment is the correct answer.

Elucidation:-

We know,

$\boxed{W = F \ • \ s \ cos (\theta)}$

where,

• W = work done,
• s = Displacement
• θ = Angle between force and Displacement.

Clearly, θ = 180°

∴ W = Fs cos(180°)

⇒ W = Fs × - 1 (∵ cos 180° = - 1)

⇒ W = - Fs

or, there is a negative work done.

If you're in IXth CBSE, use this:-

In this case, the work done is negative. This is because, the displacement is in the opposite side of force applied over the compartment.

Answer 2

Answer:

The correct answer is option b. i.e., the man does negative work on the compartment

Explanation:

Since the force applied and displacement are along a straight line in the same direction, θ =180°

As we know, work done is given by W=F.s cosθ

                                                              =F.s cos180°

Since cos180°= - 1

                                       work done is  = - F.s

Therefore, the man does negative work on the compartment