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Physics Form 4 Chapter 2 Force and Motion I

Checkpoint 2.7
Q1 A racing car with a mass of 600 kg is moving at
50 m s . Compare the magnitude of the impulsive
–1
force acting on the car if it collides with
(a) a concrete pillar and stops in 0.02 seconds,
and
(b) the concrete pillar that has old tyres covering
it so that the car is stopped in 0.2 seconds.
(c) Compare the answer in (a) and (b) and
explain the role of the old tyres.
(d) The mass of a racing car is usually smaller
than that of an ordinary car. Using Newton’s
second law of motion, explain the advantage Figure 2.93 The book dropped by the student is
of the racing car having a smaller mass. pulled towards the Earth

Q2 Figure 2.91 shows a worker receiving a
Chapter
2 watermelon thrown at him. Explain why he
moves his arms backwards when receiving the
watermelon.

Figure 2.94 Direction of the gravitational field
Figure 2.91 around Earth

Q3 (a) Explain the role of the front and rear 2. For an object with mass, m, its weight, w is
crumple zones of a car.
(b) Explain why the passenger safety cell is given by w = mg where g is the gravitational
strong and rigid. field strength.
Q4 Figure 2.92 shows the action of an air bag in 3. The SI unit for weight is newton (N). Weight
cushioning a driver during a crash. is a vector quantity.
SPM Tips

Gravitational field strength,
1 kg g at this point is equal to
the gravitational force
acting on a mass of 1 kg
Figure 2.92 placed at this point.
(a) Why does the driver more forward when the g = F
car stops suddenly? m
(b) How can the air bag save the driver from SI unit = N kg –1
serious injury?

Checkpoint 2.8
Q1 (a) Define weight and mass.
2.8 Weight (b) Give three differences between weight and
mass.
(c) What is the weight of a student on the
surface of the Earth if his mass is 47 kg?
1. The weight of an object is the force of gravity (Assume the gravitational acceleration
acting on the object. = 10 m s )
–2

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