7. Friction, Inclines, Systems

Stacked Blocks

Multiple Choice
A 4kg block sits on top of a 6kg block which is on a frictionless surface. The coefficients of friction between the two blocks are μs=0.5 and μk=0.3. Calculate the maximum force you can pull on the bottom block with so that the objects move together.
Open Question
(II) A flatbed truck is carrying a heavy crate. 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 against the cab of the truck?
Open Question
A block of mass m is at rest at the origin at t = 0. It is pushed with constant force F₀ from 𝓍 = 0 to 𝓍 = L across a horizontal surface whose coefficient of kinetic friction is μₖ = μ₀ ( 1 - 𝓍/L ) . That is, the coefficient of friction decreases from μ₀ at 𝓍 = 0 to zero at 𝓍 = L.b. Find an expression for the block's speed as it reaches position L.
Open Question
A 1500 kg car skids to a halt on a wet road where mu(k) = 0.50. How fast was the car traveling if it leaves 65-m-long skid marks?
Open Question
A baggage handler drops your 10 kg suitcase onto a conveyor belt running at 2.0 m/s. The materials are such that μₛ = 0.50 and μₖ = 0.30. How far is your suitcase dragged before it is riding smoothly on the belt?
Open Question
Sam, whose mass is 75 kg, takes off across level snow on his jet-powered skis. The skis have a thrust of 200 N and a coefficient of kinetic friction on snow of 0.10. Unfortunately, the skis run out of fuel after only 10 s.a. What is Sam's top speed?
Open Question
The 2.0 kg wood box in FIGURE P6.58 slides down a vertical wood wall while you push on it at a 45° angle. What magnitude of force should you apply to cause the box to slide down at a constant speed?
Open Question
A 50,000 kg locomotive is traveling at 10 m/s when its engine and brakes both fail. How far will the locomotive roll before it comes to a stop? Assume the track is level.
Open Question
A 1.0 kg wood block is pressed against a vertical wood wall by the 12 N force shown in FIGURE P6.57. If the block is initially at rest, will it move upward, move downward, or stay at rest?
Open Question
A large box of mass M is moving on a horizontal surface at speed v₀. A small box of mass m sits on top of the large box. The coefficients of static and kinetic friction between the two boxes are μₛ and μₖ, respectively. Find an expression for the shortest distance dₘᵢₙ in which the large box can stop without the small box slipping.
Open Question
(III) A 4.0-kg block is stacked on top of a 12.0-kg block, which is accelerating along a horizontal table at a = 5.2m/s² (Fig. 5–43). Let μₖ = μₛ = μ . <IMAGE>
(d) What is the force that must be applied to the 12.0-kg block in (a) and in (b), assuming that the table is frictionless?