In: Physics
A box is sliding on a rough surface at a constant speed. Which statement is TRUE?
1. Work done by gravity is negative
2. Friction deos not do any work
3. Work done by friction is negative
4 Work done by friction can be either positive or negative depending on direction of motion?
The right option for this Question is [4] Work Done by Friction is Negative.
When a body slides along a surface (horizontal) then the Work Done by Gravity is Zero, Which rules out option number 1.
Since the Body is sliding along a Rough surface Friction does work, which rules out Option 2.
As for option 4 , it is a little tricky. Friction can do positive work in reference to another frame. For example, If you have two block arranged on top of each other and they start acclerating , then the work done by friction on the top body is going to be positive with respect to the bottom body. So Work Done by friction is Going to be a relative tearm here, which rules out option 4 as we are considering a single frame with one moving body.
This leaves us with option 3 . As we all know friction is an opposing force, the work done by friction on the moving object is going to be negative.
Hope this Helps!!