A person standing on a scaffold lowers an object of weight 250 N by means of a rope, at constant speed. If the weight of the rope is negligible, the force that the person exerts is …

Question

A) constant and less than 250 N

B) equal to 250 N

C) less than 250 N and decreasing

D) greater than 250 N

Answer 1

Hi Dexter!

To start problems like these, we always want to draw a free body diagram to start. Luckily, there are only 2 forces acting on the rope/object here--the gravitational force (AKA weight, with a value of 250 N here) and the human's exerted force. In this case, the gravitational force is pointing straight down, and the human's exerted force is pointing straight up.

The second thing we need to notice is a golden phrase in the question--"constant speed." Constant speed means something is neither accelerating or decelerating. That means acceleration is 0. And by F=ma, if acceleration (aka a) is 0, then the net force on the object must be 0. Therefore, the 250 N weight and the human force must balance each other out perfectly, making the human force equal a constant value of 250 N, so answer choice B is the correct one here.