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Physics Form 4 Chapter 2 Force and Motion I

Checkpoint 2.5
Q1 Figure 2.68 shows two bumper cars moving in a straight line. Bumper car A 200 kg
with a total mass of 100 kg is moving at a velocity of 2 m s . Bumper car B 5 m s –2
–1
with a total mass of 200 kg is moving at a velocity of 5 m s . After a while,
–1
the two cars collide. After the collision, bumper car A moves with a velocity 2 m s –2 100 kg
of 6 m s .
–1
(a) What is the total momentum of the bumper cars before the collision? B
(b) What is the total momentum of the bumper cars after the collision?
(c) State the principle used for your answer in (b). A
(d) Calculate the velocity of bumper car B after the collision.
–1
Q2 A 1500 kg van travelling at a speed of 15 m s collides with a 1000 kg car Figure 2.68
travelling in the opposite direction with a speed of 20 m s . After the
–1
collision, both vehicles get stuck and move together. 15 m s –1 20 m s –1
(a) What is the total momentum of the van and the car before the 1 500 kg Chapter
collision? 1 000 kg
(b) What is the total momentum of the van and the car after the
collision? 2
(c) State the principle used in your answer in (b). Figure 2.69
(d) Calculate the velocity of the van and the car after the collision.
Q3 A bullet of mass 12 g is fired at a speed of 360 m s from a rifle of mass 6 kg.
–1

Figure 2.70
(a) What is the recoil velocity of the rifle?
(b) The bullet travels towards a block of wood resting on a frictionless surface. The wooden block moves with
–1
a velocity of 12 m s after the bullet is embedded in it. Calculate the mass of the wooden block.
Q4 Figure 2.71 shows two situations. Explain the observations based on the figure.

(a) (b)
Figure 2.71
(a) When water rushes out of the hose with a very high speed and volume, the fireman holding the hose needs
the support of another fireman so that he does not fall backwards.
(b) A pair of identical twins are doing ice skating. Initially, they hold each other’s hands. When they push each
other and release their hands, both of them move in opposite directions with the same speed.

2.6 Force

1. Generally, a force is the push or pull on an object as result of interaction with other objects.
2. When two objects interact, a force will act on each other.

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