Part 1: Multiple-Choice Questions

PHY111 Exam 3 Version B MacIsaac page 5

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Part 1: Multiple-Choice Questions.

These questions are worth 3 points each, and will be scored by the partial-credit scheme (correct answer in one response = 3pts, correct in 2 responses = 2pts, correct in 3 =1 pt). Please clearly mark your responses on this page. Choose the BEST answer.

1. If you exert 100 J during 200 seconds what is your power output?

A. 0.5 W B. 1.0W C. 2.0 W D. 4.0 W

2. It takes 20 W of power to push a large box 4 m across a floor in 2 seconds. Assuming the push is in the same direction as the move, what is the magnitude of the force on the box?

A. 4 N B. 10 N C. 40 N D. 50 N.

3. Two identical railroad freight cars roll towards one another other, one coming from the East at 2.5 m/s, the other from the West at 4.0 m/s. After they collide, they couple and roll together with a final speed of?

A. 0.5 m/s B. 0.33 m/s C. 0.75 m/s D. 1.0 m/s

4. A 6.0 kg bowling ball is raised 5 meters and then released. The ball falls straight down, ignoring air resistance what is the ball’s velocity when it strikes the ground?

A. 7.7 m/s B. 3.8 m/s C. 58.8 m/s D. 9.9 m/s

5. A crate with a mass of 15 kg is raised 1.25 meters by a woman and placed on a horizontally moving conveyer belt. The belt moves the crate horizontally 15 meters, then it is lowered to the ground by a man. How much work does the conveyer belt do on the crate?

A. 30 J B. 200 J C. 0 J D. -30 J.

Part II: Short Answer Questions.

These questions are worth 3 points each, and require both units and reasonably significant figures. Partial credit may be awarded for work shown.

6. [Chap 6 H.W. 13] The hammer throw is a track and field event in which a 7.3 kg ball is whirled around in a circle several times and released. In one throw the hammer is given a speed of 29 m/s. How much work is done to launch the hammer?

7. [Chap 6 H.W. 48] A basketball player makes a jump shot. The 0.600 kg ball is released at a height of 2.00 meters above the floor with a speed of 7.20 m/s. The ball goes through the net 3.00 meters above the floor at a speed of 4.20 m/s. What is the work done on the ball by air resistance, a nonconservative force?

8. [Chap 7 H.W. 20] A woman is standing at the edge of an offshore oil rig. She fires a gun and is driven backward over the edge, into the sea. Suppose the mass of the bullet is 0.010 kg, and its velocity is 720 m/s. Her mass (including the gun) is 51 Kg. What is her recoil velocity?

9 [Chap 7 H.W. 5] A volleyball is spiked so that its incoming velocity of 4.0 m/s is changed to an out going velocity of 21 m/s. The mass of the volleyball is 0.35 kg. What impulse does the player apply to the ball?

10 Two objects are placed on a horizontal rod that is 1.5 meter long and has negligible mass. M1 has a mass of 1.5 kg, and its center is located 12 cm from the left end of the rod. M2 has a mass of 4.0 kg and its center is located 18 cm from the right end. Find the center of mass.

12 cm 18 cm

M1 M2

Part III: Problem-Solving & Discussion Questions.

These questions are worth 5 points each, and all require a diagram and explanation in clear phrases or point form. Please answer them on these pages provided. Partial credit will be awarded.

11. At an icy Flagstaff intersection a car and a truck collide. The 1300 kg car enters the intersection travelling North at 2.8 m/s, and the 2900 kg truck enters moving West at 3.5 m/s. After the collision, the tangled wreckage moves off at an angle, with no lost parts.

(a) Sketch this situation on a Cartesian coordinate system with the origin in the center of the intersection. Label the car and truck, and indicate their initial velocities.

(b) Calculate and indicate initial and final momentum vectors (size and direction) on the sketch.

12. A ski resort near Flagstaff has a ski run that stretches 3.5 km, descending 800m. A 59kg skier starts from rest at the top of the ski run (3500 m above sea level). She skis down a slope and over an intermediate hill of height 3100m. During this time she loses 2.5 kJ of energy to friction and air resistance. She then skis to the foot of the run, dropping to a height of 2700m above sea level and losing another 1.5 kJ of energy to air resistance and friction.

(a) Sketch this situation. Label the top of the run, the intermediate hill and foot of the run.

(b) Write an equation showing how the skier's energy can be described at the top, intermediate hill and foot of the run. Explain it in your own words.

(d) Calculate the skier's gravitational potential energy at the three described points.

(e) Calculate the skier's momentum,at the three described points.

13. A 40m long factory conveyer belt is tilted at 30 degrees, lifting boxes from basement level to the back of a waiting truck at street level. It lifts one 10 kg box in every 1.5 seconds, and three boxes are on the belt at the same time (as one comes off the top it is replaced at the bottom)..

(a) Sketch this situation. Calculate and label the total lift of the conveyer.

(b) How much work does the conveyer belt do to lift each box? Where does this energy go?

(d) How much total power is required to drive the belt (neglect friction)?

(e) If the belt is driven by an electric motor which loses 20% of its energy to friction and heat, what is the minimum horsepower rating for this motor to drive the belt?