Page 19 - Focus TG4 KSSM (Physics) Terbitan Penerbitan Pelangi Sdn Bhd

Physics Form 4 Chapter 2 Force and Motion I

EXAMPLE 2.12 Checkpoint 2.3
Q1 What is the time taken for a stone to undergo
A student throws a stone free fall of 100 m? (Assume the gravitational
–2
vertically upwards. acceleration, g = 10 m s )
The stone moves to a Q2 Figure 2.41(a) shows an astronaut standing on
height of 5 m before the surface of the Moon. He releases a piece of
stopping and then falls paper and a rubber ball from the same height at
downwards. Figure 2.40 the same time. Figure 2.41(b) is a stroboscopic
photograph that shows how the piece of paper
shows the path moved and the rubber ball undergo free fall and reach
by the stone from A to B the ground at the same time. HOTS
and C.
(a) What is the Ball
magnitude of the Paper Chapter
velocity of the stone
when it leaves the
hand of the student? 2
(b) How long is the time (a) (b)
taken for the stone to
travel from A to C? Figure 2.41
(Take g = 10 m s ) Figure 2.40 (a) What is meant by free fall?
–2
(b) What inference can you make based on the
Solution observations?
Height, s = 5 m. (c) When the activity is repeated on the Earth,
which of the two objects will reach the
(a) The stone moves in the opposite direction from ground first? Explain your answer.
the gravitational force. Hence, the value of the Q3 Figure 2.42 shows a ball is thrown vertically
gravitational acceleration is g = –10 m s . At upwards from the position A with a velocity of
–2
–1
B, the stone come to a rest. Hence, v = 0 m s . 24 m s . The ball moves to position B, and then
–1
falls downwards.
If its speed when in A is v A , therefore by using
the formula, B
v = u + 2as
2
2
0 = v A + 2 (–10)(5)
2
v A = 100
2
Therefore, v A = 10 m s –1
(b) The displacement of the stone from A at position 24 m s –1
C is 0. By using the formula,
1
s = ut + at 2
2 A
1
0 = 10t + (–10)t 2
2
5t(2 – t) = 0
t = 2 s Figure 2.42
Hence the total time taken by the stone to travel (a) What is the distance between A and B?
(b) What is the time taken for the ball to move
from A until C is 2 seconds. from A to B?
(c) State the assumption made when doing the
calculations.
(Take g = 10 m s )
–2

35

02 FOC PHYSICS F4 3P.indd 35 29/01/2020 1:39 PM