物理 1983 年 DSE、CE 選擇題

1.

A person in a lift, which is ascending at a velocity of $10\ \mathrm{m\,s^{-1}}$ , releases a ball. What is the velocity of the ball with respect to the earth at the moment when the ball is released ?

2.

Two balls $X$ and $Y$ , of the same mass, are released from rest simultaneously at $A$ . $X$ falls vertically downwards while $Y$ runs downwards along the smooth plane $AC$ as shown in the figure. Which of the following statements is/are correct ?

(1)

X

reaches

B

at the same time as

Y

reaches

C

.

(2)The velocity of

X

at

B

is the same as that of

Y

at

C

.

(3)The kinetic energy possessed by

X

at

B

is the same as that of

Y

at

C

.

Right-angled triangle: ball X falls vertically from A to B, ball Y runs down the smooth slope AC

3.

A bullet of mass $0.01$ kg travelling horizontally at $100\ \mathrm{m\,s^{-1}}$ is stopped by $0.1$ m of concrete. What retarding force is applied to the bullet by the concrete ?

4.

A system consists of two identical masses travelling in opposite directions with equal speed. Suppose they collide elastically at time $t_0$ . Which of the following graphs correctly shows the total momentum of the system before and after the collision ?

Four graphs A to D of total momentum against time with the collision at time t0

5.

A trolley of mass $1$ kg travelling at $2\ \mathrm{m\,s^{-1}}$ on a smooth horizontal plane has a lump of plasticine dropped from a height $5$ m onto it. If the mass of the plasticine is $2$ kg, the velocity of the loaded trolley will be

6.

A student of weight $500$ N runs up a flight of stairs $15$ m high in $20$ s. The average power developed by the student is

7.

The net force acting on a particle is zero. Which of the statements below concerning the motion of the particle may be true ?

8.

The graph shows the variation of velocity $v$ with time $t$ when a metal ball is released from rest and allowed to fall vertically under gravity through oil. Which of the following statements concerning the motion of the ball is/are correct ?

(1)The velocity of the ball decreases with time.

(2)The acceleration of the ball decreases with time.

(3)The ball stops falling after

4

s.

Velocity against time graph rising from 0 and levelling off at 10 m/s by about 4 s

9.

A particle is in motion with a constant force acting on it. Which of the following physical quantities will be changing during the time when the force is acting ?

(1)acceleration of the particle

(2)momentum of the particle

(3)kinetic energy of the particle

10.

A fixed mass of gas has its temperature changed from $127^\circ$ C to $27^\circ$ C at constant pressure. The ratio of the new volume to the old volume is