Physics 9 - Quiz 1 - Winter 2001

Physics 14 - Midterm #2 - Fall 2006 a SHOW ALL YOUR WORK AND REASONING 1. (5 pts) A mass (2 kg) is initially seen to be moving horizontally at 6 m/s. You push on it, against the way it is moving, and slow it down to a speed of 4 m/s. How much work did you do on it?

If the mass moved 2.0 m while stopping, with how much force did you push on it?

2. (5 pts) You are standing in the back of a small boat that is moving forward at a constant speed. You start walking toward the front of the boat. Draw a picture of you and the boat before and after you start walking, showing velocity vectors for you and the boat at each time.

What happens to the speed of the boat when you start walking? Explain. Physics 14 - Midterm #2 - Fall 2006a Physics 14 - Midterm #2 - Fall 2006a 3. (4 pts) If a sound becomes louder, which wave characteristic is likely increasing – frequency, wavelength, amplitude, or speed? Explain.

If the sound’s pitch increases, which wave characteristic is likely increasing – frequency, wavelength, amplitude, or speed? Explain.

4. (4 pts) A ball is released from rest down three different slopes as shown. (No friction.)

C A B Rank in order the final speeds of the ball, from fastest to slowest, for the three different slopes. (For example: “A fastest, then B, then C slowest”.) Explain you answer. Physics 14 - Midterm #2 - Fall 2006a

5. (12 pts) Two footballers, Joe (m = 80 kg) and Bo (m = 100 kg), are running in opposite directions when Bo tackles Joe. Immediately after the tackle they are both at rest. Explain all your answers below.

a) Draw a diagram below showing them and their velocity vectors just before and then just after they collide.

b) Who lost the most momentum during the tackle? Explain.

c) Who felt the greatest force during the tackle? Explain.

c) Who had the greatest acceleration during the tackle? Explain.

e) If Joe had an initial speed of 5.0 m/s to the right, what was Bo’s initial speed? Physics 14 - Midterm #2 - Fall 2006a 6. (12 pts) Complete energy bar graphs for the following situations, with the initial situation at position A and the final situation being at B.: a) A mass starts from rest, touching on a compressed spring. The spring is released, and the block is pushed up over the rough surface. The block is still moving at B.

b) A sled slides from rest at A along a surface with no friction. A y = h

B y = h/2

y = 0 c) A mass, initially moving, is lowered down by a rope at constant speed for HALF the distance between A and B. Then the rope is cut so it falls freely. It is still moving at B.

rope cut

B 7. (3 pts) Two thin strips of metal (brass and iron) welded together. The picture shows them when they are at room temperature and when they are in icy water. Draw how they would look if they were dropped in hot water. Explain your answer. iron Physics 14 - Midterm #2 - Fall 2006a iron brass brass cold hot

8. (2 pts) Why did the Tacoma Narrows Bridge fall down?

9. (3 pts) What are three different reasons that a watermelon will stay cool longer than a bundle of sandwiches when both are removed from a cooler at the same time on a hot day?

10. (2 pts) What contains more internal energy, a swimming pool of water at 10°C or a cup of water at 100°C? Explain.

11. (2 pts) A metal pen and a wooden pencil are placed in a refrigerator over night. You take them out of the refrigerator in the morning and hold one in each hand. Which (if either) will become as warm as your hand faster. Explain. Physics 14 - Midterm #2 - Fall 2006a

12. (2 pts) Why is it a good idea to have your hand extended forward when you are getting ready to catch a fast-moving baseball with your bare hand?

13. (2 pts) Why do the same notes (for example, Middle C = 256 Hz) played on a piano and on a guitar sound quite different from each other?

14. (3 pts) Consider two glasses, one filled with water and the other half full of the water. The water in the two glasses is at the same temperature. In which glass are the water molecules moving faster?

In which glass of water is there greater internal energy?

In which glass will more heat be required to increase the water temperature by ten degrees Celsius?

15. (3 pts) What is a longitudinal wave? Give two physical examples of one. Physics 14 - Midterm #2 - Fall 2006a

16. (2 pts) We hear different sounds as a siren comes toward us and then moves away from us. Explain why with a diagram.

17. (2 pts) Would a head-on collision between two identical cars be more damaging to the occupants if the cars stuck together or if the cars rebounded upon impact? (Assume the time of the collision is the same.)

18. (5 pts) Draw the next two standing waves on a string stretched between two walls and label the nodes and antinodes on all three pictures.

1st harmonic

2nd harmonic

3rd harmonic Physics 14 - Midterm #2 - Fall 2006a 19. (2 pts) What is the physical difference between a loud sound and a quiet sound?

20. (2 pts) One sound has an intensity of 20 decibels and another has an intensity of 70 dB. Which one is louder and by what factor? (That is, is it 3 times as loud, 5 times as loud, etc?)

21. (4 pts) You apply a force of 25 N to a 1.5 kg mass and it moves in the direction of your push a distance of 5.0 m in a time of 20 seconds. How much work do you do on the mass?

What is your power output while you push?

22. (3 pts) You have two different mass balls – one is 2.0 kg and the other is 4.0 kg. Describe all the things you must know in order to predict successfully which ball will hit the ground first. Physics 14 - Midterm #2 - Fall 2006a

23. (6 pts) Add together the two waves below to find their combined wave form.

-2 2 1

4 3 2 1

-1 -2 -3 -4

FORMULAE:

f  m a m v

2 dװf = 1/ T K = ½ mv Ug = mgy W = F