Distance and Speed : Scalar Quantities and Displacement and Velocity: Vector Quantities
1. Distance is always (a) equal to the magnitude of the corresponding, (b) less than or equal to the magnitude of the
corresponding displacement, (c) greater than or equal to the magnitude of the corresponding displacement. (c)
2. Two people choose different reference points to specify and object’s position. Does this difference affect the
coordinates of the object? How about its displacement? Explain.
3. You are told that a person walks 500 m. What can you safely say about the person’s final position relative to the
starting point? (no final position can be given; may be 0 to 500m from start)
4. A motorist drives 150 km from one city to another in 2.5 h but makes the return trip in only 2.0 h. What are the
average speeds for (a) each half of the round trip and (b) the total trip? (a) 60 km/h, 75 km/h (b) 67 km/h
5. A senior citizen walks 0.30 km in 10 min going around a shopping mall. What is her average speed in meters per
second? (b) If she wants to increase her average speed by 20% in walking a second lap, what would her travel time in
minutes have to be? (a) .50 m/s (b) 8.3 min
6. A boy runs 30 m east, 40 m north, 50 m west. What is his net displacement? 45 m at 27° west of north
7. A student throws a ball vertically upward such that it travels 10 m to its maximum height. If the ball is caught at the
initial height 2.4 s after being thrown, (a) what is the ball’s average speed? (b) Its average velocity? (a) 8.3 m/s (b) zero,
displacement zero
8. (a) Given that the speed of sound is 340 m/s and the speed of light is 3.00 x 10 8 how much time will elapse between a
lightning flash and the resulting thunder, if the lightning strikes 2.50 km away from the observer? (b) does your answer
change if you assume light travels with an infinite speed (that is, the lightning flash is seen instantaneously)? (a) 7.35 s
(b) no
9. A race car travels a complete lap on a circular track of radius 500 m in 50 s. (a) what is the average speed of the race
car? (b) what is the average velocity of the race car? (a) 63 m/s (b) zero
10. In driving the usual route to school, a student computes his average speed to be 30 km/h. In a hurry to get home
that afternoon, he wants to average 60 km/h for the round trip. What would his average speed for the return trip over
the same route have to be in order to do this? (Hint: see example 2.3, and be ready for a surprise.)