Physics 201 MWF10:20 Fall 1999 (Ford)

Exam III Chapts. 8-11 in Cutnell and Johnson 4th ed.

Multiple Choice questions. Circle the correct answer. No work needs to be shown.

1. A wheel is rotating about an axis through its center. Point A is on the rim and point B is midway between the rim and the axis.

(2 pts) Let _A and _B be the angular velocities of point A and B. Which statement is correct:

(a)  _A > _B
(b)  _A = _B <---ANS
(c)  _A < _B


(2 pts) Let v_A and v_B be the tangential velocities of point A and B. Which statement is correct:

(a)  v_A > v_B <---ANS
(b)  v_A = v_B
(c)  v_A < v_B


(3 pts) Let a_cA and a_cB be the centripetal accelerations of point A and B. Which statement is correct:

(a)  a_cA > a_cB <---ANS
(b)  a_cA = a_cB
(c)  a_cA < a_cB


(3 pts) 2. Suppose the ice cap at the South pole melted and the water was distributed uniformly over the earth's oceans. Would the earth's angular velocity of rotation about its axis

(a)  increase
(b)  remain the same
(c)  decrease <---ANS


3. You are floating in a canoe in the middle of a swimming pool. With you in the canoe you have a basketball and a bowling ball.

(3 pts) If you toss the basketball into the water, it floats. If you toss the basketball into the water, what happens to the level of water in the pool?

(a)  rises
(b)  drops
(c)  remains the same <---ANS

(3 pts) If instead you toss the bowling ball into the water, it sinks. If you toss the bowling ball into the water, what happens to the level of water in the pool?

(a)  rises
(b)  drops <---ANS
(c)  remains the same


On the following five problems show all your work. Partial credit will be given if earned. Write your answers in the blanks provided.

(14 pts) 4. The front and rear sprockets on a bicycle have radii r₁ = 12.0 cm and r₂ = 3.0 cm, respectively. The bicycle chain passes over both sprockets. The angular velocity of the front sprocket is 5.0 rad/s. What is the angular velocity of the rear sprocket?

Ans. ___20 rad/s____


(17 pts) 5. A solid cylinder (I = MR²/2 for rotation about an axis through its center) is released from rest at the top of an incline, at a vertical distance of 3.0 m above the floor. The mass of the cylinder is 0.40 kg. As the cylinder travels down the hill it rolls without slipping. What is the rotational kinetic energy, I²/2, of the cylinder when it reaches the floor?

Ans. _____3.92 J_____


(18 pts) 6. A uniform rod weighing 200 N is attached to a wall by a hinge. The rod is held by a horizontal cable so that the rod makes an angle of 37° with the wall. Calculate the tension in the cable.

Ans. ____75.4 N______


(18 pts) 7. A block of mass 2.0 kg is attached to a horizontal spring. The block oscillates back and forth on a horizontal frictionless surface and makes 5.0 completes cycles in 3.0 s. The maximum speed of the block during its motion is 4.0 m/s. What is the amplitude of the motion? (The amplitude is the maximum displacement of the block from its equilibrium position.)

Ans. _____0.382 m______

(17 pts) 8. A rock has mass 2.0 kg and density 5000 kg/m³. When the rock is suspended by a string and totally submerged in a liquid, the tension in the string is 15.0 N. What is the density of the liquid?

Ans. ____1.17 × 10³ kg/m³_____