F2 IS 2nd Term WS04 9.4B Answers

2nd Term WS 04 Submission date：_____________ Name：______________________ Class & no.：2 _________(     )

9.4 B    Action and reaction (P.28-32)

i     Words to know:

	English term	Write the words again	Chinese term
1	Action-reaction pair		作用力和反作用力
2	Equal		相同
3	Opposite		相反
4	Eject		噴射
5	Launch		發射
6	Overcome		克服

i     Fill in the blanks:

1      When an object exerts a force on another object, it experiences an equal force in the

         opposite direction at the same time. These two forces are called an      action-reaction pair.

2      During a rocket launch, a large amount of hot gas is ejected downwards

from the rocket. The ejected gas produces an equal force that pushes the rocket upwards.

The great pushing force overcome the force of gravity acting on the rocket.

3       During a water rocket launch, the water is ejected downwards from the rocket. The ejected

         water produces an equal force that pushes the water rocket upwards.

i     Multiple choice: Circle the letter of the best answer for each question.

1.      When an inflated balloon is released, it will fly away. We can explain this in terms of

A. Friction                B. action and reaction               C. weightlessness                     D. gravity

2.       What forces does a rocket have to overcome when it is launched from Earth?

(I)                 Force of gravity

(II)               The pushing force due to the hot gas coming out from the rocket engine

(III)             Air resistance

A. (I) only                  B. (III) only                   C. (I) and (II) only                 D. (I) and (III) only