Page 52 - Schaum's Outline of Theory and Problems of Applied Physics

CHAP. 3] MOTION IN A STRAIGHT LINE 37

SOLVED PROBLEM 3.16
The driver of a car traveling at 50 m/h applies the brakes and the car decelerates at a constant rate. What
is the velocity of the car 0.8 mi farther along the road if the car reaches this point 1.2 min after the brakes
were applied?

Here t = 1.2 min = (1.2/60)h = 0.02 h. Since
v 0 + v

s = t
2
the final velocity is

2s
v = − v 0
t
2(0.8mi)
= − 50 mi/h = (80 − 50) mi/h = 30 mi/h
0.02 h

Multiple-Choice Questions

3.1. In which of the following examples is the motion of the car not accelerated?
(a) A car turns a corner at the constant velocity of 20 km/h.
(b) A car climbs a steep hill at the constant velocity of 20 mi/h.
(c) A car climbs a steep hill with its velocity dropping from 60 km/h at the bottom to 20 km/h at the top.
(d ) A car climbs a steep hill and goes over the top and then down on the other side, all at the same velocity of
40 km/h.

3.2. A snail travels 45 cm in 20 min. Its average velocity is
(a) 2.25 cm/h (c) 90 cm/h
(b) 15 cm/h (d ) 135 cm/h

3.3. A car travels at 20 km/h for 1.5 h, at 30 km/h for 2.0 h, and at 40 km/h for 0.75 h. The car’s average velocity is
approximately

(a) 19 km/h (c) 28 km/h
(b) 21 km/h (d ) 30 km/h

2
3.4. How long does a bicycle with an acceleration of 0.8 m/s take to go from 4 to 12 m/s?
(a) 6.4 s (c) 15 s
(b) 10 s (d )26 s

2
3.5. A car that starts from rest has a constant acceleration of 4 m/s . In the first 3 s the car travels
(a) 6 m (c) 18 m
(b) 12 m (d )72 m

3.6. An airplane starting from rest takes 25 s and 500 m of runway at constant acceleration to leave the ground. Its velocity
when it becomes airborne is

(a) 20 m/s (c) 40 m/s
(b) 32 m/s (d ) 80 m/s
2
3.7. A car has an acceleration of 1.2 m/s . If its initial velocity is 10 m/s, the distance the car covers in the first 5 s after the
acceleration begins is