Physics 111, Exam 3A A

Physics 111, Exam 3A A Part I. Put the answers to these 12 questions on your SCANTRON sheet. Your answer should be CLOSEST TO THE GIVEN

1) An 1800-kg car stopped at a traffic light is struck from the rear by a 900 -kg car and the two become entangled. If the smaller car was moving at 20m/s before collision, what is the speed of the entangled mass after the collision? a) 6.67 m/s b) 0 m/s c) 10.23 m/s d) 0.67 m/s e) 300 m/s

2) A body of mass 2.0-kg makes an elastic collision with another body at rest and continues to move in the original direction but with one fourth (1/4) of its original speed. What is the mass of the other body? a) 4.2-kg b) 1.2-kg c) 3.7-kg d) 0.6-kg e) 29-kg

3) Two titanium spheres approach each other head on with the same speed and collide elastically. After the collision, one of the spheres, whose mass is 300-g, remains at rest. What is the mass of the other sphere? a) 0.6-kg b) 0.1-kg c) 1.5-kg d) 2.9-kg e) 10.2-kg

4) What is the magnitude of the angular velocity of a spaceship taking a circular turn of radius 3220 km at a speed of 29000 km/h? a) 200 rad/h b) 0.1 rad/h c) 49 rad/h d) 9 rad/h e) 15 rad/h

5) The angular position of a point on the rim of a rotating wheel is given by   4.0t  3.0t 2  t 3 , where  is in radians and t in seconds. What is the average angular acceleration for the time interval that begins at t = 2s and ends at t = 4s? a) 200 rad/s2 b) 12 rad/s2  c) 0.1 rad/s2 d) 5 rad/s2 e) 34 rad/s2

6) A disk, initially rotating at 120 rad/s, is slowed down wit a constant angular acceleration of magnitude 4.0 rad/s2. How much time does the disk take to stop? a) 0.1 s b) 130 s c) 90 s d) 30 s e) 0.3 s

1 Physics 111, Exam 3A A 7) A flywheel with diameter of 1.2 m is rotating at an angular speed of 200 rad/min. What constant angular acceleration will increase the wheel’s angular speed to 1000 rad/min in 60 s? a) 800 rad/min2 b) 92.5 rad/min2 c) 0.8 rad/min2 d) 200 rad/min2 e) 5 rad/min2

8) The body in figure 1 is pivoted at O, and two forces act on it as shown. If r1=1.30 m, r2=2.15 m, F1=4.20 N, F2=4.90 N, 0 0 1 = 75 and 2 = 60 . What is the net torque about the pivot? a) 7.29 Nm b) -3.85 Nm c) -7.29 Nm d) 3.85 Nm e) 342.5 Nm

9) The rigid body shown in figure 2 consists of three particles connected by massless rods. M=0.4 -kg, a=30 cm and b=50cm. What is the rotational inertia of the rigid body about an axis perpendicular to its plane through point P? a) 13.6-kg m2 b) 5.93-kg m2 c) 125-kg m2 d) 0.75-kg m2 e) 0.136-kg m2

10) A small ball with mass 1.3-kg is mounted on one end of a thin, uniform rod 0.78 m long and of mass 7.8-kg. The system rotates in a horizontal circle about the other end of a rod. What is the rotational inertia about the axis of rotation? a) 9.42-kg m2 b) 7.32-kg m2 c) 2.37-kg m2 d) 0.92-kg m2 e) 50.21-kg m2

11) What is the rotational inertia of a wheel that has a kinetic energy of 24400 J when rotating at 602 rev/min? a) 0.92-kg m2 b) 12.30-kg m2 c) 112.3-kg m2 d) 18.9-kg m2 e) 121.20-kg m2

12) If a 32.0 N m torque on a wheel causes angular acceleration of 25 rad/s2, what is the wheel’s rotational inertia? a) 5.64-kg m2 b) 1.28-kg m2 c) 3.40-kg m2 d) 200-kg m2 e) 22.39-kg m2

2 Physics 111, Exam 3A A Part II. Workout Problems. To get partial credit you must show your work.

1) (2 points) A bullet of mass 10 g strikes a ballistic pendulum of mass 2-kg. The center of mass of the pendulum rises a vertical distance of 12 cm. Assuming that the bullet remains embedded in the pendulum, calculate the bullet’s initial speed.

2) (3 points) In Figure 3, one block has mass M=0.5-kg, the other has mass m=0.46-kg, and the pulley, which is mounted in horizontal frictionless bearings has a radius of 0.05 m. When released from rest, the more massive block falls 0.75 m in 5 s (without the cord slipping on the pulley). What is: a) The magnitude of the blocks’ acceleration? b) The tensions T1 and T2? c) Magnitude of pulley’s angular acceleration? d) The rotational inertia?

3 Physics 111, Exam 3A A

1a,2b,3b,4d,5b,6d,7a,8b,9e,10c,11b,12b workout 1 V=308.25 m/s 2 2 workout 2 a=0.06 m/s; T1= 4.57 N; T2= 4.87 N;  =1.2 rad/s ; I=0.014 -kg m