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The speed of the ambulance is 60 km/h and the car is stationary. What is the speed of the ambulance as measured by a person in the car? vA 60 km/h 0 km/h > 60 km/h < 60 km/h km 60 < > 60 km km /h 0% /h 0% /h 0% 0 km /h 0% 60 1. 2. 3. 4. 1 The ambulance is stationary and the car is travelling at 60 km/h. What is the speed of the ambulance as measured by a person in the car? vC 60 km/h 0 km/h > 60 km/h < 60 km/h km 60 < > 60 km km /h 0% /h 0% /h 0% 0 km /h 0% 60 1. 2. 3. 4. 2 The speed of sound in still air is 340 m/s. The speed of the ambulance is 60 km/h and the car is stationary. What speed of sound does a person in the car measure? vA 340 km/h 0 km/h > 340 km/h < 340 km/h km 34 0 < > 34 0 km km /h 0% /h 0% /h 0% 0 km /h 0% 34 0 1. 2. 3. 4. 3 The speed of sound in still air is 340 m/s. The ambulance is stationary and the car is moving at 60 km/h. What speed of sound does a person in the car measure? vc 340 km/h 0 km/h > 340 km/h < 340 km/h km 34 0 < > 34 0 km km /h 0% /h 0% /h 0% 0 km /h 0% 34 0 1. 2. 3. 4. 4 The speed of light is c. The speed of the ambulance is c/2 and the car is stationary. What speed of light does a person in the car measure? vA c 0% c 0% < 0% > 0% 0 c 0 >c <c c 1. 2. 3. 4. 5 The speed of light is c. The ambulance is stationary and the car is moving at c/2. What speed of light does a person in the car measure? vC c 0% c 0% < 0% > 0% 0 c 0 >c <c c 1. 2. 3. 4. 6 If you were traveling with respect to the stars close to the speed of light, you could detect it because Your mass would increase Your heart would slow down You would shrink … all of the above You could never tell your speed by changes in you 0% 0% 0% 0% 0% Yo ur m as s Yo w ou ur ld he in ar c. tw .. ou ld sl Yo o. u .. w ou ld … sh al ri n l Yo of k u th co e ul ab d ov ne e ve rt el l. .. 1. 2. 3. 4. 5. 7 A spear 10 m long is thrown at a relativistic speed through a pipe that is 10 m long. Both the dimensions are measured when each is at rest. When the spear passes through the pipe, which of the following statements best describes what is observed? de pe n d. .. s. .. eq ua lly An y of t he se , . t.. k so sh rin Bo th Any of these, depending on the motion of the observer. sh rin ks 4. 0% 0% 0% 0% so ... Both shrink equally so that the pipe just covers the spear at some instant. pi pe 3. sh rin ks The pipe shrinks so that the spear extends from both ends at some instant. Th e 2. sp ea r The spear shrinks so that the pipe completely covers it at some instant. Th e 1. 8 According to observes on Earth, it takes 2 years for a rocket to travel to a nearby star . According to observes on the rocket, what time has passed?. The speed of the rocket is v and its Lorentz factor is 1 v2 1 2 c v 1. 2 years 2. 2 / years 3. 2 years 9 When the rocket arrives at the star, what time interval do observers on the rocket measure for a clock located on the Earth. v 1. 2. 3. 4. 2 years 2 / years 2 / 2 years 2 years 10 A rocket leaves Earth and travels to a nearby star at speed v (corresponding to a Lorentz factor = 3) relative to observes on Earth. According to clocks on the rocket, the journey takes 2 years. If the Earth and the star are in the same rest frame (clocks are synchronized) what do clocks on the star read when the rocket arrives? v 0% ye ar s ye ar s 0% 2 ye ar s 0% 2/ 3 6 years 2 years 2/3 years 6 1. 2. 3. 11 Dr Chris is standing near the middle of a falling board. Dr Chris said that the two ends of the board hit the ground at the same time and therefore must be horizontal. But Prof Pat (who is running past the falling board at near the speed of light) said that the end B hit the ground first, before the other end A and therefore the board was tilted towards the right. Dr Chris 0% he Fa ls e: t Prof Pat bo ar d bo ar d is ca n n. . ho ... 0% he 2. True: the board is horizontal for one observer and tilted for another observer. False: the board can not be horizontal and tilted at the same time. Tr ue :t 1. 12 c/2 f of r: fast train (S’) Prof Pat A’ O’ B’ A O B f of r: ground (S) Dr Chris AO = OB A’O’ = O’B’ According to Prof Pat at O’ all the train clocks (A’ O’ B’) are synchronised and all ground clocks (A O B) are synchronised. Dr Chris knows she is midway between A & B locations. Lightning strikes each end of the train and the ground together in 2 separate events A/A’ and B/B’. Dr Chris at O receives the flashes from A & B at the same time when the flashes happen and works out that her clock read 10 am when the flashes happened. When Prof Pat’s clock reads 10 am, she is exactly level with Dr Chris whose clock also reads 10 am. 13 What is the time on the ground clock A when the lightning strikes? 1. before 10 am 2. 10 am 3. after 10 am 10 0% am am 0% af te r1 0 be fo re 10 am 0% 14 What is the time on the ground clock B when the lightning strikes? 1. before 10 am 2. 10 am 3. after 10 am 10 0% am am 0% af te r1 0 be fo re 10 am 0% 15 What is the time on the train clock A’ when the lightning strikes? 1. before 10 am 2. 10 am 3. after 10 am 10 0% am am 0% af te r1 0 be fo re 10 am 0% 16 What is the time on the train clock B’ when the lightning strikes? 1. before 10 am 2. 10 am 3. after 10 am 10 0% am am 0% af te r1 0 be fo re 10 am 0% 17 A comet is chasing a spacecraft. Let v be the speed of, p the momentum and K the kinetic energy of the comet as perceived by the astronaut when it hits the spacecraft. In what way would increasing the speed of the spacecraft alter the astronaut’s perceived values of v, p and K? no tc ha ng w ill e. .. v, al l p de w cr ill ea de se cr v, . ea K se w ill ,K de w cr K, ... ea p se w ill ,p de w cr ... ea se ,v w ... ill v, p, K 5. 0% 0% 0% 0% 0% w 4. v, p, K will not change at all. v, p, K will all decrease. v, p will decrease, K will not change. v, K will decrease, p will not change. K, p will decrease, v will not change. v, p, K 1. 2. 3. 18 A rocket ship in space emits brief flashes of light from its beacon at a steady rate of 1 flash every 6 min rocket time. These flashes are observed on a distance planet. If the rocket ship approaches the planet at near light speed, observes will see the flashes at intervals 0% 6 6 m in m in 0% th an th an 6 m in 0% m or e less than 6 min 6 min more than 6 min le ss 1. 2. 3. 19 A rocket ship that emits flashes of light every 6 min travels between two planets, A and B. It travels away from A and towards B. If the flashes are seen at 3 min intervals on B, then on planet A the flashes are seen at in m 12 m 0% in te rv al s in te rv al s 0% in in te rv al s 0% in m 6 m in in te rv al s 0% 9 3 min intervals 6 min intervals 9 min intervals 12 min intervals 3 1. 2. 3. 4. 20 Our rocket ship departs from the Earth at noon & travels at the same near light speed for 1 hour rocket time. During this hour it emits a flash every 6 min, 10 in all. An Earth observer sees these flashes at 12 min intervals. When the 10th flash is received on Earth, clocks on Earth read o’ cl oc k 0% 2: 30 2: 00 1: 30 0% o’ cl oc k 0% o’ cl oc k 0% o’ cl oc k 1:00 o’clock 1:30 o’clock 2:00 o’clock 2:30 o’clock 1: 00 1. 2. 3. 4. 21 Our rocket ship is able to abruptly turn around when it emits its 10th flash and then returns to Earth at the same near light speed. It continues sending flashes every 6 min and emits 10 flashes in its hour of return. The rocket ship’s clock reads 2:00 o’clock when it gets back to Earth. What time will a clock on Earth read? 0% o’ cl oc k o’ cl oc k 0% 2: 30 2: 00 o’ cl oc k 0% 3: 00 also 2:00 o’clock 2:30 o’clock 3:00 o’clock al so 1. 2. 3. 22 Suppose an atomic bomb was exploded in a box that was strong enough to contain all the energy released by the bomb. After the explosion the box would weight 0% di d th e. .. be ... 0% Th e sa m e as it be fo re th an The same as it did before the explosion ex p. .. 3. Le ss Less than before the explosion be fo re 2. th an More than before explosion M or e 1. 0% 23 The celebrated equation E = m c2 or m = E / c2 tells us how much mass loss m must be suffered by a nuclear reactor in order to generate a given amount of energy E. Which of the following statements is correct? 0% eq ua t Th e e E = io n m c2 ap pl ie s or .. .. 0% sa m 2. The same E = m c2 or m = E / c2 also tells us how much mass loss m must be suffered by a flashlight battery when the flashlight puts out a given amount of energy E. The equation applies to nuclear energy in a reactor, E= m c2 but not to chemical energy in a battery. Th e 1. 24 Consider a motor bike powered with powerful electric batteries and an electric trolley car that are each driven near light speed. Measurements of each from our rest frame will indicate an increase in the mass of 0% ne ith er y 0% bo th 0% ca r 0% tro lle motor bike trolley car both neither m ot or bi ke 1. 2. 3. 4. 25