Laws of Motion: Friction

1. A dockworker is loading 20.2-kg crates onto a ship. He notices that it takes 77.2 Newtons of horizontal force to set them into motion from rest. Once in motion, it takes 58.3 Newtons of horizontal force to keep them moving at a constant speed. Determine the coefficient of static friction. Enter your answer accurate to the third decimal place.

(Referring to the previous problem.) Determine the coefficient of kinetic friction. Enter your answer accurate to the third decimal place.

2. A box rests on the back bed of a truck. The coefficient of friction between the box and the surface is .789. Calculate the maximum acceleration (in m/s/s) that the truck can have before the box will slide along the truck bed.

3. Consider the free-body diagram shown at the right. If the applied force is 58.1 N at an angle of 23 degrees, the force of gravity is 127.2 N and the coefficient of friction is .626, then what is the acceleration (in m/s/s) of the object. Is it a negative value for a leftward acceleration?

4. A box of books weighing 304 N is shoved across the floor of an apartment by exerting a force of 443 N downward at angle of 35.2 degrees below the horizontal . If the coefficient of kinetic friction is .572, how long (in seconds) does it take the box to move 2.99 meters.

5. A man doing his spring cleaning pulls a 151-N vacuum cleaner across the floor at a constant velocity of 1.13 m/s by exerting a force on it at an angle of 35.4 degrees above the horizontal. If he must pull with a force of 35.5 N to move the vacuum cleaner, what is the coefficient of friction between the vacuum cleaner and the floor? Enter your answer accurate to the fourth decimal place.

6. A student slides a 1323 N crate across the floor by pulling with a force of 761 N at an angle of 30.8 degrees with the horizontal. If the crate moves at a constant speed, find the coefficient of sliding friction between the crate and the floor. Enter your answer accurate to the fourth decimal place.