Question

what happens when a force is applied to an object while the object moves in a direction opposite to the force?a. negative work is doneb. work is done only if the force causes a decrease in speedc. positive work is doned. work is done only if the force causes an increase in speed.

Answer 1

A constant force applied to an object moving in a rectilinear trajectory does the following work:

$W=Fd\cos\theta$

where F is the magnitude of the force, d is the distance the object moved and θ is the angle between the force and the displacement vector. In this case we know that the object is moving in a direction opposite to the force applied, this means that the angle between them is 180°, since the cosine of this angle is -1, this means that the work done will be negative.

Therefore, the correct option is a.