4.3 You are driving in one direction on a long straight road. You drive in the positive direction at 126 km/h for 30.0 minutes, at
which time you see a police car with someone pulled over, presumably for speeding. You then drive in the same direction at
100 km/h for 45.0 minutes. (a) How far did you drive? (b) What was your average velocity in kilometers per hour?
(a) km
(b) km/h4.4 You made a journey, and your displacement was +95.0 km. Your initial velocity was +167 km/h and your final velocity was
í26.0 km/h. The journey took 43.0 minutes. What was your average velocity in kilometers per hour?
km/h4.5 The first controlled, sustained flight in a heavier-than-air craft was made by Orville Wright on December 17, 1903. The plane
took off at the end of a rail that was 60 feet long, and landed 12 seconds later, 180 feet away from the beginning of the rail.
Assume the rail was essentially at the same height as the ground. (a) Calculate the average velocity of the plane in feet per
second while it was in the air. (b) What is the average velocity in kilometers per hour?
(a) ft/s
(b) km/h4.6 A horse is capable of moving at four different speeds: walk (1.9 m/s), trot (5.0 m/s), canter (7.0 m/s), and gallop (12 m/s). Ann
is learning how to ride a horse. She spends 15 minutes riding at a walk and 2.4 minutes at each other speed. If she traveled
the whole way in the positive direction, what was her average velocity over the trip?
m/s4.7 A vehicle is speeding at 115 km/h on a straight highway when a police car moving at 145 km/h enters the highway from an
onramp and starts chasing it. The speeder is 175 m ahead of the police car when the chase starts, and both cars maintain
their speeds. How much time, in seconds, elapses until the police car overtakes the speeder?
sSection 5 - Instantaneous velocity
5.1 The tortoise and the hare start a race from the same starting line, at the same time. The tortoise moves at a constant
0.200 m/s, and the hare at 5.00 m/s. (a) How far ahead is the hare after five minutes? (b) How long can the hare then snooze
until the tortoise catches up?
(a) m
(b) s5.2 You own a yacht which is 14.5 meters long. It is motoring down a canal at 10.6 m/s. Its bow (the front of the boat) is just
about to begin passing underneath a bridge that is 30.0 m across. How much time is required until its stern (the end of the
boat) is no longer under the bridge?
s
5.3 The velocity versus time graph of a unicycle is
shown. What is the instantaneous velocity of
the unicycle at (a) t = 1.0 s, (b) t = 3.0 s, and
(c) t = 5.0 s?
(a) m/s
(b) m/s
(c) m/s
5.4 Two boats are initially separated by distance d and head directly toward one another. The skippers of the boats want to arrive
at the same time at the point that is halfway between their starting points. Boat 1 moves at a speed v and boat 2 moves at
twice the speed of boat 1. Because it moves faster, boat 2 starts at time t later than boat 1. The skippers want to know how
much later boat 2 should start than boat 1. Provide them with an equation for t in terms of d and v.
t = d/4v
t = 3d/2v
t = 3d/4v
t = d/2v5.5 This problem requires you to apply some trigonometry. A friend of yours is 51.0 m directly to your left. You and she start
running at the same time, and both run in straight lines at constant speeds. You run directly forward at 5.00 m/s for 125 m.
She runs to the same final point as you, and wants to arrive at the same moment you do. How fast must she run?
m/s