Question

A woman at an airport is towing her 10kg suitcase at constant speed by pulling on the strap at an angle of 30 above the horizontal. She pulls on the strap with a 40.0 N force. A) What is the force of friction? B) What normal force does the ground exert on the suitcase?

Answer 1

Let,

• : be the mass of the suitcase
• : be the force she pulls on the strap
• : be the friction force or force of kinetic friction.
• : be the normal force.
•     : be the acceleration due to gravity.
•     : be the angle with horizontal.

Given:-

• 
• 
• 
• 

Below figure shows free body diagram of the suitcase and the forces acting on it.

The pulling force F must resolve into its x and y components.

x-component of the force F i.e. along horizontal direction is given as,

y-component of the force F i.e. along vertical direction is given as,

A) The force of friction :-

From the figure, the forces along x-direction i.e. horizontal direction are force of friction and pulling force which are opposite in direction.

The friction force and x-component of the pulling force balance each other.

Therefore,

This is the friction force or the force of kinetic friction.

B) Normal force :-

The forces along y-direction or along vertical direction are :

• normal force along positive y-direction.
• y-component of the pulling force along positive y-direction.
• Weight along negative y-direction.

These three forces should balance such that,

This is the normal force the ground exert on the suitcase.