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Physics Form 4 Chapter 2 Force and Motion I

SPM Highlights HOTS Checkpoint 2.1
A cat sees a rat running towards a hole with a uniform Q1 Farid leaves his home at 10:00 am and walks to
velocity 0.4 m s . At that time the position of the cat, the the post office to post a letter. After that, he walks
–1
rat and the hole are shown in the diagram respectively. If to a bookstore to buy a present. From there, he
the cat runs towards the rat with a uniform acceleration walks to KEC Fried Chicken to pack some food
–2
of 1.0 m s , can the cat catch the rat before it enters before going to Ken’s house to celebrate his
the hole? birthday. Farid reaches Ken’s house at 12:00
noon.

1.8 km
0.9 km
Farid’s Post office
house U Chapter
6.0 m 2.0 m B T
1.2 km
Bookstore
Figure 2.21 S 2
0.7 km
1.6 km
Answer:
Distance between the cat and the hole is 8.0 m and Ken’s house KEC Fried
distance between the rat and the hole is 2.0 m. If Chicken
time taken for the cat to reach the hole is longer than
the time taken for the rat to reach the hole, the cat Figure 2.22
will not able to catch the rat or vice versa. By the time Farid reaches Ken’s house,
(a) what is the total distance travelled?
For the rat, its uniform velocity, (b) what is his average speed?
v = 0.4 m s –1
s = 2.0 m (c) calculate his displacement.
(d) calculate his average velocity.
Since
s = v × t for uniform velocity, Q2 Figure 2.23 shows four strips of ticker tapes
t = s
v HOTS obtained from an experiment using a trolley.
2.0
=
0.4
= 5.0 s End Beginning
Tape P
For the cat,
initial velocity, u = 0 m s –1 Tape Q
acceleration, a = 1.0 m s –2
displacement, s = 8.0 m Tape R
Using the formula Tape S
1
s = ut + at , Figure 2.23
2
2
1
8.0 = 0 + (1.0)t 2
2 (a) Compare tape P with tape Q and describe
t = 16.0 (i) one common characteristic,
2
Therefore, t = 16.0 (ii) one difference between them.
= 4.0 s (b) Describe the motion of the trolley for
(i) tapes R,
Since the rat needs 5.0 s to reach the hole while the (ii) tapes S.
cat needs only 4.0 s, the cat will be able to catch the
rat before it enters the hole.

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02 FOC PHYSICS F4 3P.indd 27 29/01/2020 1:39 PM