物理 1987 年 DSE、CE 選擇題

1.

A ball moving in a smooth horizontal plane hits against a wall and rebounds perfectly elastically. Which of the following graphs best represents the variation of kinetic energy with time ?

2.

Which of the following is/are correct unit(s) for momentum ?

(1)

\mathrm{kg\,m\,s^{-1}}

(2)

\mathrm{kg\,m\,s^{-2}}

(3)N s

3.

Which of the following statements is/are true ? A man in a lift feels heavier when the lift is moving

(1)upwards with acceleration.

(2)upwards with retardation.

(3)downwards with retardation.

4.

An escalator is said to be able to carry $120$ passengers to a height of $10$ m in one minute. Assuming each passenger has a weight of $500$ N, the possible power output by the escalator must be at least

5.

An object is projected vertically upwards. Which of the graphs below correctly describes the variation of its kinetic energy ( $KE$ ) with height ( $h$ ) ?

Four graphs A to D of KE against height h

6.

Graph of displacement against (time)^2: straight line from the origin to 4 m at 4 s^2

An object is accelerated from rest along a straight line. The above graph shows the variation of its displacement with the square of time. What is the acceleration of the object ?

7.

A mass of $3$ kg initially at rest explodes into two fragments $X$ and $Y$ of masses $1$ kg and $2$ kg respectively. What is the ratio of the kinetic energy of $X$ to that of $Y$ just after the explosion ?

8.

Light rod with a 2 kg mass at the left end, fulcrum F 2 cm from it, then points P (1 cm from F), Q (1 cm further) and R (2 cm further)

If a mass of $2$ kg is placed a distance of $2$ cm from the fulcrum $F$ as shown in the diagram, which of the following cases could keep the light rod in equilibrium ?

(1)a mass of

4

kg placed at

P

(2)a mass of

2

kg placed at

Q

(3)a mass of

1

kg placed at

R

9.

Wave on a string at t = 0.000 s and at t = 0.025 s

The above figures show a wave in the same section of string at two different instants. What is the greatest possible period of the wave ?

10.

The figure shows a stationary water wave at its maximum vibration. What is the direction of the motion of a particle $P$ at this instant ?

One cycle of a stationary wave with point P on the right-hand crest side