Involving Friction and the coefficients of friction Practice Problems Involving Friction and the coefficients of friction

Warm-up: A 10.0 kg box rests on a horizontal floor. The coefficient of static friction is 0.400, and the coefficient of dynamic friction is 0.300. Determine the maximum amount of static friction that will keep the box at rest. Determine the amount of force necessary to keep the box moving at a constant rate.

#2 Your little sister wants you to give her a ride across the snow on a sled (mass of both combined is 50.0 kg). The coefficient of static friction between the sled and the snow is 0.0500, and the coefficient of dynamic friction is 0.0300. What force would you need to apply to start her sliding if you were pushing down and forward at an angle of 25.0° to the horizontal? What force, at that angle, would keep her moving at a constant speed? What force would you need to apply to start her sliding if you were pulling her by a rope upwards and forward at an angle of 25.0° to the horizontal? What force, at that angle, would you need to pull to keep her moving at a constant speed?

#3 A 65.0 kg skier is sliding down a 30.0° slope. Assume the coefficient of dynamic friction between her skis and the snow is 0.0900. Determine the following: The force of friction acting on her as she slides on her skis Her acceleration down the slope How fast will she be going after 4.50 s?

#4 A 25.3 kg box filled with books was set down on a ramp of a moving van that makes an angle of 35.0° with the horizontal. If the ramp was made to be any steeper than this, the box would slide. What is the coefficient of static friction acting on the box? Assume the box would slide at a constant rate if the ramp were lowered to 27.5° once the box was in motion. What is the coefficient of dynamic friction between the box and the ramp?

#5 If the coefficient of static friction between a 35.0 kg box and a ramp is 0.45, what is the maximum angle the ramp can be above the horizontal so that the box will not move? If the coefficient of dynamic friction between that same box and ramp is 0.30, at what angle will the box, once moving, continue sliding at a constant velocity?

#6 A force of 40.0 N is required to start a 5.20 kg box moving across a horizontal concrete floor. What is the coefficient of static friction between the box and the floor? If you keep pushing the box with a constant 40.0 N horizontal force, the box will accelerate at 0.850 m·s-2. What is the coefficient of dynamic friction?

#7 A flatbed truck is carrying a heavy crate (mass = 675 kg). The coefficient of static friction between the crate and the bed of the truck is 0.75. What is the maximum rate at which the driver can decelerate and still avoid having the crate slide across the bed into the cab of the truck?

#8 A box is given a push so that it slides across the floor. How far will it go along the horizontal floor after you stop pushing? Assume that the coefficient of dynamic friction between the box and the floor is 0.25 and the box is sliding at 4.4 m·s-1 at the time you stop pushing.