A Block Sliding Down an Incline

[PrideofPhilly]

Homework Statement

Starting from rest, a 5 kg block slides 2.5 m down a rough 30 degree incline. The coefficient of kinetic friction between the block and the incline is 0.436. The acceleration of gravity is 9.8 m/s2.

Find the work done by the force of gravity.

Find the work done by the normal force.

Homework Equations

Wgravity = mgh

The Attempt at a Solution

I figured out work done by force of gravity:

Wgravity = (5 kg)(9.8 m/s2)(2.5sin30) = 61.25 J

However, I don't know how to find the work done by the normal force. Is it the same as work done by gravity?

 

[LowlyPion]

There is another force involved - friction.

 

[nlightner]

I would like to commend you for attempting to solve this problem and for seeking clarification on the concept of work done by the normal force.

To answer your question, the work done by the normal force is not the same as the work done by gravity. The normal force is the perpendicular force exerted by the surface on the block, and its work is zero because it is always perpendicular to the displacement of the block. Therefore, the work done by the normal force is equal to zero.

To better understand this concept, think of it this way: when you push a book across a table, you are applying a force parallel to the table's surface. The normal force exerted by the table is perpendicular to the surface, and it does not contribute to the displacement of the book. Thus, the work done by the normal force is zero.

In this scenario, the normal force is balancing out the force of gravity acting on the block, allowing it to slide down the incline. The work done by the normal force is simply maintaining the block's equilibrium and preventing it from falling through the incline.

I hope this explanation helps you understand the concept of work done by the normal force. Keep up the good work in your scientific endeavors!