Question

1.You are driving slowly on the highway at 50 mph when a police car with its lights flashing passes you going 100 mph. Relative to you, the police officer is moving 50 mph. Far in the future, when humans have mastered space travel, an astronaut is moving in a spaceship at half the speed of light, v = c/2, relative to earth, when a light beam sent from earth moving parallel to the spaceship passes it moving at v = c. The astronaut measures the light beam to be moving at

a.

v = c/2.

b.

v = 2c.

c.

v = 3c/2.

2.Your physics professor is foolishly standing out in a field during a thunderstorm and measures two bolts of lightning to hit two trees at opposite ends of the field at exactly the same time. You, being considerably less foolish, are driving by in a car on a road right next to the field at a speed v when the lightning bolts strike the trees, one of which is in front of the car, the other of which is behind it. You happen to line up with the professor right when he observes the lightning bolts strike the trees. As measured by you in the car,

a.	the lightning bolts do not hit both trees.

b.	the lightning bolts do not hit the trees at the same time.

Answer 1

Ans

1

The speed of the light is c in all inertial frames. So, the astronaut measures the light beam moving at speed v = c.

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2

You are moving toward the thunderbolt in front of you. The wavefronts from that bolt(in front of you) will reach you before the bolt striking the tree behind you. According to you, the lightning bolts do not hit the trees at the same time.