物理 1992 年 DSE、CE 選擇題

1.

Which of the following displacement-time graphs describes the motion of a particle moving in a straight line with uniform deceleration ?

Four displacement-time graphs A to D: A straight line falling to zero; B straight line through the origin; C curve rising with decreasing slope; D curve rising with increasing slope

2.

Equilateral triangle ABC of side 3 m with arrows along AB and BC

A man takes $2$ s to walk from point $A$ to point $B$ , and then takes $3$ s to walk from point $B$ to point $C$ , where $ABC$ is an equilateral triangle of side $3$ m. Find the magnitude of his average VELOCITY from $A$ to $C$ .

3.

A man at the edge of a cliff above the sea, and a velocity-time graph falling linearly from 60 m/s at t = 0 through zero at 6 s to -120 m/s at 18 s

The above figure shows a man near the edge of a cliff projecting a stone vertically upwards. The stone reaches the sea after $18$ s. The graph shows the velocity - time for the motion of the stone. Find the height of the cliff. (Take $g = 10$ m s $^{-2}$ .)

4.

A trolley of mass $2$ kg moves with a uniform speed of $4\ \mathrm{m\,s^{-1}}$ along a horizontal table. A lump of plasticine having the same mass as the trolley is dropped from a height slightly above the trolley and sticks to it. Find the total loss in kinetic energy.

Lump of plasticine above a trolley on a horizontal table

5.

Smooth curved rail with points A, B, C and D; ball released from rest at the left end at the level of D

A ball is released from rest from one end of a smooth curved rail as shown in the above diagram. Neglecting air resistance and friction, which of the following statements about the motion of the ball is/are correct ?

(1)The ball has maximum kinetic energy at point

B

.

(2)The speed of the ball at point

C

is the same as that at point

A

.

(3)The ball would not rise to a level higher than point

D

.

6.

Which of the following involve(s) an energy transfer of $100$ J ?

(1)A mass of

10

kg is raised vertically by

10

m.

(2)A mass of

2

kg gains a speed of

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

from rest.

(3)A

10

W heater is switched on for

10

s.

7.

Block X on a smooth table joined by a string over a pulley to hanging block Y

Two identical blocks $X$ and $Y$ are connected by a light string passing over a smooth pulley as shown above. The two blocks are released from rest. After a while, the string breaks. Which of the following correctly describes the motion of the blocks immediately after the string breaks ? (Take the acceleration due to gravity to be $10\ \mathrm{m\,s^{-2}}$ .)

	$X$	$Y$
	stops moving	accelerates at $5\ \mathrm{m\,s^{-2}}$
	moves with constant velocity	accelerates at $5\ \mathrm{m\,s^{-2}}$
	moves with constant velocity	accelerates at $10\ \mathrm{m\,s^{-2}}$
	decelerates at $5\ \mathrm{m\,s^{-2}}$	accelerates at $10\ \mathrm{m\,s^{-2}}$

8.

Block B (3 kg) and block A (2 kg) joined by string S on a smooth table, 2 N force pulling A to the right

In the diagram above, blocks $A$ and $B$ are connected by a light inextensible string and rest on a smooth horizontal table. The masses of $A$ and $B$ are $2$ kg and $3$ kg respectively. Block $A$ is pulled by a force of $2$ N. Find the tension in the string $S$ .

9.

Which of the following pairs of forces $F_1$ and $F_2$ is/are action and reaction pair(s) according to the Newton's third law of motion ?

Three cases: (1) block on the floor, F1 weight of the block and F2 reaction from the floor; (2) ball hanging on a string, F1 weight of the ball and F2 tension of the string; (3) negative and positive charges attracting each other, F1 and F2 electric forces

10.

Light rod PQRST with equally spaced points: 1 N upward at Q, 2 N downward at R, 1 N downward at S

The diagram shows a light rod under the action of three vertical forces. The points $P$ , $Q$ , $R$ , $S$ and $T$ are equally spaced along the rod. At which point must an upward vertical force of $2$ N be applied to hold the rod in equilibrium ?