Chapter 2, Problem 35A

Alyssa pulls horizontally on a crate with a force of 200 N, and it slides across the floor at a constant speed in a straight line. How much friction is acting on the crate?

To determine

Friction force acting on the crate.

Answer to Problem 35A

Friction force acting on the crate is $f=200\text{N}$

Explanation of Solution

Given:

Force exerted by person A, $F=200\text{N}$

The crate is moving at constant speed.

Formula Used:

For a system in dynamic mechanical equilibrium, the net force is zero.

Mathematically, $\sum F=0$

Calculation:

Since, the crate is moving at constant speed. It means it is in dynamic equilibrium. The crate is in dynamic mechanical equilibrium, so the sum of all the forces on it will be zero.

As the force of friction will always be in opposite direction of motion or the tendency of motion.

So, using $\sum F=0$

  $\begin{array}{l}F-f=0\\ \Rightarrow f=F\\ =200\text{N}\end{array}$

Conclusion:

Therefore, the friction force acting on the crate is 200 N.