Page 176 - Physics

Physics for Secondary Schools
Example 8.3
A ball is dropped from a height of 20 m
above the ground. It hits the ground in
2 s and bounces back up to a height of
12.7 m in 1.6 s (see Figure 8.4). What
is its average velocity?
Solution
When the object is moving up its
displacement is positive and when
moving down it is negative.
s = -20 m
t = 2 s
s = +12.7 m
t = 1.6 s
Figure 8.4
Total displacement,
s (–20 m + 12.7 ms =
s = –7.3 m
The negative sign shows the net
displacement is downwards.
Total time,
t = 2 s + 1.6 s = 3.6 s
s 6. What are the differences and
v =
t similarities between the following
- 7.3 m
= =
3.6s
=- 2.03 m/s
The negative sign shows the direction
of the velocity is downwards.
Therefore, the average velocity for the
entire motion is 2.03 m/s downwards.
170
Physics Form 1 Final.indd 170
Exercise 8.1
1. (a) Why does the average speed of
a car which travels 6 000 m in
30 s differ from its actual
speed?
(b) Calculate the average speed of
the car in (a).
2. What is the average speed of an
athlete who runs 1 500 m in
4 minutes?
3. A bus increases its speed steadily
from 20 m/s to 30 m/s in one minute.
(a) What is its average speed during
this time?
(b) How far does it travel while
increasing its speed?
4. A car moves 8 km due south and
then suddenly changes its direction
)
and moves another 6 km due west.
Determine:
(a) the total distance covered.
(b) the displacement of the car.
5. A bus travelled 180 km in 4 hours.
What was the speed of the bus?
pairs of terms?
(a) Speed and velocity.
(b) Distance and displacement.
Student’s Book Form One
16/10/2024 20:58