Physics friction problems?

Question

1. A horizontal force of 5.5 lb is required to start a sled weighing 20 lbs on which there is a child weighing 40 lbs. Find the coefficient of static friction.

∑x = 0 F = 5.5 lbs

∑y = 0 N = 20 + 40 60lbs

f = µsN therefore: µs = f / N

µs = 5.5lbs/60lbs = 0.0917

2. A 45 kg box sits on the floor. The coefficient of static friction between the block and the floor is 0.40. What magnitude of horizontal pushing force is needed to make the box slide?

3. A police examining a scene of an accident observe a skid marks 30m long left by a 1200kg car. The car skidded to a stop on a concrete highway having a coefficient of kinetic friction with the tires of 0.80. Estimate the car’s speed at the beginning of the skid.

4. A 200lb crate lies on the floor. The coefficient of static friction between the crate and the floor is 0.60. What is the minimum force required to start the crate sliding?

5. A 60kg student sitting on a hardwood floor does not slide until pulled by a 240N horizontal force. Calculate the coefficient of static friction between the student and the floor.

6. A 1kg body is projected on a level surface with horizontal speed of 1.35m/s. The coefficient of sliding friction is 0.20. Find a) how long it takes the body to come to rest and b) how far the body travels.

7. A 900kg car traveling at 20m/s skids to a stop on a wet surface after the brakes are applied. How far does the car skid if the coefficient of kinetic friction is 0.40?

Please include the solution for the problems..Thanks..

Answer 1

Much for me to answer everything. =)