Conceptual Physics

5.19 - Interactive checkpoint: moving the couch

While rearranging your living room,

you push your couch across the floor

at a constant speed with a horizontal

force of 69.0 N. You are using special

pads on the couch legs that help it

slide easier. If the couch has a mass

of 59.5 kg, what is the coefficient of

kinetic friction between the pads and

the floor?

Answer:

μk =

5.20 - Sample problem: friction and tension

Above, you see a block accelerating to the right due to the tension force applied by a rope. What is the magnitude of tension the rope applies to the block?

Starting this type of problem with a free-body diagram usually proves helpful. Draw a free-body diagram

Variables

What is the strategy?

Draw a free-body diagram.

Find an expression for the net force on the block.

Substitute the net force into Newton’s second law to find the tension.

Are there any useful relationships? Since the surface is horizontal, the amount of normal force equals the weight of the block.

The coefficient of kinetic friction is

0.200. What is the magnitude of the

tension force in the rope?

x component ycomponent normal force 0 FN = mg

acceleration a = 2.20 m/s^20

tension T 0

friction force ífk 0

mass m = 1.60 kg

coefficient of kinetic friction μk = 0.200