PHYSICS 211, Exam # 2 March 22, 2013 (Dr. Xinhua Bai’s session)
Student Name: ______(print your name neatly!)
Student ID: ______
Open book. No notes are allowed. You may use a calculator. There are twelve multiple-choice problems. For each of the multiple-choice questions below, choose the most correct answer.
1. A stone is tied to a string and whirled at constant speed in a horizontal circle. The speed is then doubled without changing the length of the string. Afterward the magnitude of the acceleration of the stone is:
A) the same
B) twice as great
C) four times as great
D) half as great
E) one-fourth as great
2. A particle moves at constant speed in a circular path. The instantaneous velocity and instantaneous acceleration vectors are:
A) both tangent to the circular path
B) both perpendicular to the circular path
C) perpendicular to each other
D) opposite to each other
E) none of the above
3. A motor boat can travel at 10 km/h in still water. A river flows at 5 km/h west. A boater wishes to cross from the south bank to a point directly opposite on the north bank. At what angle must the boat be headed?
A) 27° E of N
B) 30° E of N
C) 45° E of N
D) 60° E of N
E) depends on the width of the river
4. An object moving at constant velocity in an inertial frame must:
A) have a net force acting on it
B) eventually stop due to gravity
C) not have any force of gravity acting on it
D) have zero net force acting on it
E) have no frictional force acting on it
5. Two blocks are connected by a string and pulley as shown. Assuming that the string and pulley are massless, the magnitude of the acceleration of each block is:
A) 0.049 m/s2
B) 0.020 m/s2
C) 0.0098 m/s2
D) 0.54 m/s2
E) 0.98 m/s2
6. A ball with a weight of 1.5 N is thrown at an angle of 30° above the horizontal with an initial speed of 12 m/s. At its highest point, the net force on the ball is:
A) 9.8 N, 30° below horizontal
B) zero
C) 9.8 N, up
D) 9.8 N, down
E) 1.5 N, down
7. A 40-N crate rests on a rough horizontal floor. A 12-N horizontal force is then applied to it. If the coefficients of friction are ms = 0.5 (static) and mk = 0.4 (kinetic), the magnitude of the frictional force on the crate is:
A) 8 N
B) 12 N
C) 16 N
D) 20 N
E) 40 N
8. A 400-N block is dragged along a horizontal surface by an applied force F as shown. The coefficient of kinetic friction is μk = 0.4 and the block moves at constant velocity. The magnitude of F is:
A) 100 N
B) 150 N
C) 200 N
D) 290 N
E) 400 N
9. An 800-N passenger in a car, presses against the car door with a 200 N force when the car makes a left turn at 13 m/s. The (faulty) door will pop open under a force of 800 N. Of the following, the least speed for which the man is thrown out of the car is:
A) 14 m/s
B) 19 m/s
C) 20 m/s
D) 26 m/s
E) 54 m/s
10. An object is constrained by a cord to move in a circular path of radius 0.5m on a horizontal frictionless surface. The cord will break if its tension exceeds 16N. The maximum kinetic energy of the object can have is:
A) 4 J
B) 8 J
C) 16 J
D) 32 J
E) 64 J
11. Camping equipment weighing 6000 N is pulled across a frozen lake by means of a horizontal rope. The coefficient of kinetic friction is 0.05. How much work is done by the campers in pulling the equipment 1000 m if its speed is increasing at the constant rate of 0.20 m/s2?
A) –1.2 ´ 106 J
B) 1.8 ´ 105 J
C) 3.0 ´ 105 J
D) 4.2 ´ 105 J
E) 1.2 ´ 106 J
12. When a certain rubber band is stretched a distance x, it exerts a restoring force of magnitude F = Ax, where A is a constant. The work done by a person in stretching this rubber band from x = 0 to x = L is:
A) AL2
B) A + 2L
C) A + 2L2
D) A/L
E) AL2/2