A 200-kg box is placed on a ramp. As one end of the ramp is raised, the box begins to move downward just as the angle of inclination reaches 18.0. What is the coefficient of static friction between box and ramp?
a. 0.42
b. 0.32
c. 3.1
d. 0.27
e. 62
[Ques. 2] A horizontal force of 850 N is needed to overcome the force of static friction between a level floor and a 350-kg crate. If g = 9.8 m/s2, what is the coefficient of static friction?
a. 24.8
b. 2.48
c. 4.04
d. 0.248
e. 2.43
[Ques. 3] What forces are included in a free-body diagram for an object?
a. The forces acting on the object and the forces the object exerts on any other objects it is in contact with.
b. The forces acting on the object and the forces the object exerts on all other objects in the system.
c. Only the forces acting on the object.
d. Only forces internal to the object.
[Ques. 4] A crate of weight w is being pushed across a horizontal surface by a force directed at an angle of 20 below the horizontal. What is the magnitude of the normal force on the crate?
a. It is less than w.
b. It equals w.
c. It is more than w.
d. None of the above since the coefficient of kinetic friction is not given.
[Ques. 5] A block is launched up an incline plane. After going up the plane, it slides back down to its starting position. The coefficient of friction between the block and the plane is 0.3 . The speed of the block when it reaches the starting position on the trip down:
a. is the same as the launching speed.
b. is less than the launching speed.
c. is more than the launching speed.
d. cannot be compared to the launch speed with the information given.
[Ques. 6] A block is launched up an incline plane. After going up the plane, it slides back down to its starting position. The coefficient of friction between the block and the plane is 0.3 . The time for the trip up the plane:
a. is the same as the time for the trip down.
b. is more than the time for the trip down.
c. is less than the time for the trip down.
d. cannot be found without knowing the angle of inclination.
[Ques. 7] A hockey puck moving at 7.00 m/s coasts to a halt in 80.0 m on a smooth ice surface. What is the coefficient of friction between the ice and the puck?
a. = 0.109
b. = 0.031
c. = 0.063
d. = 0.094
e. = 0.156
[Ques. 8] A worker pulls a 350-N packing crate at constant velocity across a rough floor by exerting a force F = 200.0 N at an angle of 30.0 above the horizontal. What is the coefficient of kinetic friction of the floor?
a. 0.793
b. 0.693
c. 0.593
d. 1.386
e. 0.400
[Ques. 9] Dana uses a rope to pull a box that weighs 600 N across a level surface with constant velocity. The rope makes an angle of 40 above the horizontal and the tension in the rope is 400 N. What is the coefficient of friction?
a. 0.89
b. 0.88
c. 2.00
d. 1.19
e. 0.84
[Ques. 10] Jamal pulls a 250-N sled up a 29.0 slope at constant speed by a force of 200 N. Near the top of the hill he releases the sled. With what acceleration does the sled go down the hill?
a. 7.84 m/s2
b. 9.30 m/s2
c. 3.32 m/s2
d. 1.66 m/s2
e. 2.66 m/s2
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