Active Physics Chapter 3 Practice Test

1. B-29 Pilots during WWII would sometimes run into high altitude (40,000 ft) headwinds of 75 mph. Today we know these headwinds as the jet streams. The B-29 aircraft had a cruising speed of 230 mph.
   1. From the frame of reference of a crew member what is the speed of the plane's pilot?
   2. If the B-29 were to fly past a hot air balloonist, what is the speed of the plane's pilot from the frame of reference of the hot air balloonist ?
   3. From the frame of reference of a ship on the ocean below the plane what is the speed of the plane's pilot?
2. The gravitational force between two asteroids is 400 N. N is the abbreviation for Newton, the metric system unit of force. If the distance between the asteroids is doubled what is the gravitational force?
3. Mike is shining a flashlight on a photoelectric cell. If he wants the light intensity (brightness) on the cell to be 4 times greater how much closer does he need to get to the sensor?
4. What is the relationship between Sir Isaac Newton and the motion of the planets?
5. Draw two waves (one above the other) that will add destructively.
6. If the distance to Coupeville is 15 miles and you drive at 30 mph, how long will it take you to go to Coupeville?
7. If the distance to Mars is 225,000,000,000 m and the speed of light is __________ how long will it take for the light to go to Mars? Hint: you will probably have to use scientific notation.

Active Physics Chapter 3 Practice Test Answers

1. B-29 Pilots during WWII would sometimes run into high altitude (40,000 ft) headwinds of 75 mph. The B-29 aircraft had a cruising speed of 230 mph.
   1. From the frame of reference of a crew member the pilot is not moving. Speed = 0 mph.
   2. From the frame of reference of the hot air balloonist the speed of the plane's pilot is 230 mph.
   3. From the frame of reference of a ship on the ocean the speed of the plane's pilot is 230 mph - 75 mph = 155 mph.
2. The gravitational force between two asteroids is 400 N. If the distance between the asteroids is doubled, the gravitational force is 100N. The strength of gravity fields follow the inverse square law rule. This means that doubling the distance makes the field 1/4 as strong. Tripling the distance makes the field 1/9 as strong. Expressed mathematically below:

   At the beginning: 400N · ( 1/distance²) = 400N · (1/1²) = 400 N

   Doubling the distance:400N · (1/2²) = 400N · (1/4) = 100 N

3. Light intensity also follows the inverse square law. If Mike wants the light intensity on the cell to be 4 times greater he must reduce the distance to the sensor by 1/2. Hint: make a t-table of distance and intensity.
4. Newton used his law of universal gravitational attraction to better explain the motion of the planets.
5. Draw two waves that will add destructively.
6. If the distance to Coupeville is 15 miles and you drive at 30 mph, how long will it take you to go to Coupeville? Time = distance / speed = 15 miles / 30 mph = 1/2 hr or 30 minutes.
7. If the distance to Mars is 225,000,000,000 km and the speed of light is __________ how long will it take for the light to go to Mars?

   Time = distance / speed = 225,000,000,000 m / 300,000,000 m/s = 750 s

   Time = distance / speed = 2.25 · 10¹¹ m / 3 · 10⁸ m/s = 750 s     or 7.5 · 10² s