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I) Multiple choice (11 questions, 5 points each)
1) / A mass m is placed on a rough incline. A force F is applied to the mass in a direction up the incline. The magnitude of the force is just enough to prevent the mass from sliding down. Which arrow best represents the direction of the friction? /A) / (a) / D) / (d)
B) / (b) / E) / (e)
C) / (c)
2) / A woman drives her car at a speed of 25 m/s around a un-banked corner. The coefficients of friction between the road and the tires are 0.70 (static) and 0.40 (kinetic). What is the minimum radius of curvature for the corner in order for the car not to skid?
A) 3.5 102 m B) 64 m C) 2.1 102 m D) 1.6 102 m E) 91 m
3) / The Earth has mass 5.97 1024 kg. The moon has mass 7.35 1022 kg. The distance between the centers of the Earth and the Moon is 3.84 105 km. How far from the center of Earth is the center of mass of the Earth–moon system?
A) / 4.67 103 km / D) / 2.11 105 km
B) / 7.42 103 km / E) / 3.84 103 km
C) / 1.92 105 km
Use the scenario below for the next two questions.
A 5.00-kg object slides down a frictionless surface inclined at an angle of 30.0º from the horizontal. The total distance moved by the object along the plane is 10.0 meters.
4) / The work done on the object by the normal force of the surface is
A) zero B) 490 J C) 427 J D) 583 J E) 245 J
5) / The work done on the object by the force of gravity is
A) 245 J B) 425 J C) 42.5 J D) 43.3 J E) zero
6) / A girl runs up the stadium steps. Her mass is 80.0 kg, and it takes one minute for her to run up the 120 steps at a constant rate. If each step is of height 0.250 m, what is her power output?
A) 9600 W B) 40.0 W C) 1570 W D) 392 W E) 235 W
Use the picture to the right to answer the next two questions.
A 6.0-kg block slides from rest at position A down a frictionless incline to position B. After the block passes point B, a friction force opposes the motion of the block so that it comes to a stop 2.5 m from B. /
7) / The speed of the block at B is
A) 3.1 m/s B) 4.4 m/s C) 11 m/s D) 1.8 m/s E) 20 m/s
8. / Calculate the coefficient of kinetic friction between the block and the surface after position B.
A) 2.5 B) 0.40 C) 0.070 D) 0.65 E) 3.8
9. / A toy car of mass 2.0 kg moving to the right with a speed of 8.0 m/s collides perfectly inelastically with another toy car of mass 3.0 kg that is moving to the left with a speed of 2.0m/s. Immediately after the collision the velocity of the system is
A) / 4.4 m/s to the right. / D) / 2.0 m/s to the left.
B) / 2.0 m/s to the right. / E) / 10 m/s to the left.
C) / 0 m/s
10. / Glider A, traveling at 10.0 m/s on an air track, collides elastically with glider B traveling at 8.0m/s in the same direction. The gliders are of equal mass. The final speed of glider B is
A) 8.4 m/s B) 10 m/s C) 8.0 m/s D) 4.0 m/s E) 12 m/s
11. / A ball of mass m strikes a wall that is perpendicular to its path at speed v and rebounds in the opposite direction with the same speed. If you define the positive direction to be away from the wall (in the same direction as the velocity of the ball immediately after the collision), the impulse imparted to the ball by the wall is
A) –2mv B) –mv C) zero D) mv E) 2mv
PHYS 121BMidterm 2, Practice