Chapter 3 Linear Motion
Exercises
3. The average speed would be the total distance/total time (including breaks and stops). What does a trooper measure with his radar gun average or instantaneous?
4. Remember:
 | Speed is measured by a speedometer, and |
| Velocity is measured by a speedometer and a compass. |
10. Remember:
| Velocity is measured by a speedometer and a compass, and |
| By definition, acceleration is the change in velocity. |
16. Think of the bus moving at a constant speed – when would it accelerate? Can you have acceleration if the bus has constant velocity?
18. Which has velocity and acceleration in different directions (compass):
| Bus speeding up, or |
| Bus slowing down |
19. Match the diagrams to the effect of the shape:
| Constant acceleration, |
| Acceleration decreases with time, or |
| Acceleration increases with time. |
25. What does the change in velocity (speed) each second describe? Is it constant for each second? What is the value? See Free Fall p. 47.
26. Can the distance for successive time intervals stay the same with constant acceleration? See page 49.
27. Look back to # 25. Would this change in velocity change or be constant? What is the value for g at the end of 5th second? End of 10th second?
29. Look back to #18. Acceleration can be the opposite of velocity. If g is the opposite of the velocity how much will the ball slow each second? Once velocity is zero, how much will the ball accelerate coming down? What is the up time compared to the down time?
30. For the ball that is thrown up, you need to determine the speed of the ball when it returns back to the starting position. Knowing that speed you can compare the speed of the two balls when they strike the ground. Hint: Compare the speed, not which one hits first! See page 50.
32. Is the value of g different for an object that is dropped vs. an object that is thrown down?
40. Think about which ball would have the greater average speed! The ball with the higher average speed would finish first.
Problems
1. 2000 years. Hint: Set the two ratios equal and solve for the unknown years. Convert 3 m to mm!
2. –10 km/h/sec. Hint: Use the equation on page 46.
4. Hint: look at figure 3.9 and answer the questions. (a) 0 m/s, (b) 10 m/s – the value of g , (c) 10 m/s – the value of g , (d) -10 m/s – same as 1 second before, but opposite direction, (e) 10m/s – the value of g, (f) 20 m/s, (g) 10 m/s2 toward the earth.
5. (a) v = g * t = 100 m/s, (b) vavg = (vf + vi)/2 = 50m/s, (c) d = vavg * t = 500 m
6. a = (vf - vi)/time = 2.5 m/s2, d =½ a * t2 = 125 m
7. 240 km/h Hint: total distance/total time
10. t = .35 s and hang time = .70 s