Physics 10 Midterm 1 1. What property of waves, did the project Mogul rely on? A. interference B. beats Mogul project use the sound channel, C. bending on slow side look again at Chapter 7 of book ** D. dispersion most missed question E. None of the above 2. The asteroid that hit our planet last fall never made it to the ground and yet, many windows were shattered and some building collapsed. What could have cause the damage? Sound waves is the only thing A. Earthquakes that could have travelled and B. Sound waves carried the energy away. C. Heat D. Light waves. 3. The velocity of sound Higher temperature means higher kinetic energy and A. increases when the temperature increases higher speed of molecules. This B. decreases when the temperature decreases results in higher speed of C. depends on the concentration of carbon dioxide in the sound air D. is constant independent of the temperature 4. How does the mass and electric charge of a proton compare to that of an electron. A. same mass, same charge B. proton has the bigger mass and they have opposite charge C. electron has the bigger mass and they have opposite charge D. proton has the bigger mass and they have the same charge E. electron has the bigger mass and they have opposite charge Partial credit 3points if you had one right and the other wrong (mass and charge) 5. A skateboarder skates along a ramp shaped like a “W” starting at point A, as shown below. His total energy (gravity and kinetic) at point A is 1500 J. Assuming no loss of energy to friction, what is his total energy at point C? A.
B.
C.
D.
E.
Keyword is total energy. 1500 J Total energy does not change! 2500 J 0 J Impossible to calculate without the skater’s mass and velocity Impossible to calculate without the skater’s gravitational energy Partial credits 3 points for D or E 6. A mosquito flaps its wings 680 vibrations per second, which produces the annoying 680 Hz buzz. The speed of sound is 340 m/s. How far does the sound travel between wing beats? A. 2 m B. 0.5 m λ = v/f = 340/680 = 0.5 m C. 231200 m D. 0.00147 m 7. When a car is brought to a stop by braking, its kinetic energy is transformed to A. Stopping energy Not potential energy. All the B. Potential energy kinetic energy when you broke C. Energy of motion goes into heat of tire, break and D. Heat energy raod. You can’t get it back. 8. A table has the same temperature as the air above it. That means that the molecules in the air and in the table have Not velocity!! Kinetic energy A. The same average velocity B. The same average kinetic energy C. The same average acceleration D. The same average mass Partial credits 3 points for A, very common misconception 9. At a constant temperature, for a mixture of hydrogen gas, oxygen gas, and nitrogen gas, the molecules with the greatest average speed are those of Same temperature means same A. Hydrogen average kinetic energy but this B. Oxygen means that the lowest mass C. Nitrogen D. all have the same average speed atom will move faster. Partial credits 3 points for D, very common misconception that follows from Q8 10. In order to light up a 30 Watt light bulb for 10 seconds, how much energy must be used assuming that there is no loss (100% efficient)? 30 Watt times 10 Seconds = A. 300 Joules 300 Joules B. 600 Joules C. 1500 Joules D. 6 Joules 11. Which of the following graphs describes simple periodic motion with amplitude 2 cm and frequency 0.5 Hz. Frequency of 0.5 Hz means a period of 2 second. In E, the period between two peaks is 2 second. Amplitude of 2 cm means that the waves goes between -­‐2cm and +2 cm Correct answer is E. I gave partial credit of 3 points for A, C, and B for getting amplitude or period right 12. If you vibrate one end of a string at a frequency f the waves travel at a speed V and have a wavelength L. If you were to vibrate that end of the string at twice that frequency (2f), the speed and V = λ f wavelength would be: The key part here is that V does A. V, 2L not change if I change f or λ. B. 2V, L C. V, L/2 Double f D. 2V, L/2 Half λ E. V, L Such that v is unchanged I gave partial credit of 4 points for D, 3 points of B. 13. In order for two sound waves to produce audible beats, it is essential that the two waves have: A. the same number of harmonics B. slightly different amplitudes C. slightly different harmonics D. slightly different frequencies 14. We can say an object is at rest in a fundamental, universal sense when: A. We don’t see it move. There is no such as an ultimate B. It doesn’t move relative to the surface of the Earth point of view. There is no sense C. It doesn’t move relative to the center of the Earth in which something is at rest in D. It doesn’t move relative to the sun a fundamental sense. E. We can’t ever say that. I gave partial credit of 3 points for A and B because of common misconceptions. 15. Is it possible, according to Einstein's relativity, for a child to be biologically older than his or her parents? A. Yes, if the child goes on a very long and fast trip and then returns to the Earth. B. Yes, if the parents go on a long and fast trip and then return to the Earth C. No, It is not possible to go "back" in time. D. No, relativity does not affect biological aging Clocks really run slower. The slow one is the one moving. So I gave partial credit of 5 points for A because its very close you want to send the parents away in order for their clock to slow down. Your parents could come back younger than you. They will still be older than when they left. This is not traveling back in time. 16. Since there is an upper limit on the speed of a particle, does it follow that there is also an upper limit on its kinetic energy? Explain and make sure to mention what your answer implies for conservation of energy. No! Very few people got this right. There is not upper limit on kinetic energy. The equation for kinetic energy K = ½ mv2 must be wrong at high speed. (it is replaced by E2 = (mc2)2+p2c2). There cannot be a limit on energy because if there were, how would energy be conserved? 17. Discuss one of the news articles we have seen in Unit 1. In brief, what was the story? What was the physics behind the headlines? Many good possible answers here, do try to find the physics behind the article.