Question

If a machine exerts a force of 250 N on an object and no work is done, what must have occurred?

Answer 1

Answer:

1) There is no work done by the machine because

B) The object has not moved

2) There is no work done by the prisoner because

D) The prisoner does no work because the wall goes no distance

3) The kinetic energy when it is half the way down is

6.0 J

Explanation:

1) As we know that the work done is the product of force and displacement

It is given as

$W = Fdcos\theta$

so if the object is not displaced due to the force exerted by the object then the work done by the object must be ZERO

so correct answer is

B) The object has not moved

2) As we know that the work done is the product of force and displacement

It is given as

$W = Fdcos\theta$

As we know that the wall is not displaced due to applied force so here work done by the prisoner must be zero

D) The prisoner does no work because the wall goes no distance

3) As we know by work energy theorem that work done by all forces is equal to change in its kinetic energy

So we will have

$W_g + W_f = \frac{1}{2} mv^2$

so we will have

$3(10)(4) + W_f = \frac{1}{2}(3)(3)^2$

$120 + W_f = 13.5$

$W_f = -106.5 J$

now when cart moves half the distance then again using the same

$W_g + W_f = K$

$K = 3(10)(2) - \frac{106.5}{2}$

$K = 6.5 J$