物理 2002 年 DSE、CE 選擇題（第 2 頁）

11.

Grace and Kitty, of masses $50$ kg and $40$ kg respectively, stand on light rollers on a smooth horizontal floor. They are initially at rest with Grace holding a $2$ kg ball. Grace throws the ball to Kitty and moves backward with a speed $0.8\ \mathrm{m\,s^{-1}}$ afterwards. After catching the ball, Kitty moves in the opposite direction as shown. Which of the following statements is/are correct ?

(1)The final speed of Kitty is

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

.

(2)The horizontal momentum of the ball is conserved in this process.

(3)The total kinetic energy of Kitty and the ball decreases when Kitty catches the ball.

Grace moving left at 0.8 m/s and Kitty (holding the ball) moving right, both on rollers on a smooth floor

12.

Ray striking the slanted side of a parallelogram glass block

A ray of light travels in air and strikes a glass block as shown above. Which of the following diagrams best shows the path of the ray ?

Four ray diagrams A to D through the glass block

13.

Temperature against time graph for crushed solid: rising, flat melting section, then rising again

A certain amount of crushed solid is heated and the variation of its temperature $T$ with time $t$ is shown above. If the same heater is used to heat a smaller amount of the solid, which of the following graphs (in dash lines) best shows the variation of the temperature of the solid ?

Four graphs A to D, each with the original curve (solid line) and a new curve (dashed line)

14.

Questions 20 and 21 : The specific heat capacity of a metal is measured using the following method :

Step 1: metal block heated in boiling water in a beaker. Step 2: block transferred to a cup of cold water with a thermometer

A metal block is first immersed in boiling water for some time. The block is then transferred to a cup of cold water. After a while, the temperature of the water is measured.

The result of the experiment is as follows : Mass of metal block $= 0.8$ kg Mass of water in the cup $= 0.3$ kg Initial temperature of water in the cup $= 23^\circ\mathrm{C}$ Final temperature of water in the cup $= 38^\circ\mathrm{C}$ Find the specific heat capacity of the metal (in $\mathrm{J\,kg^{-1}\,{}^\circ C^{-1}}$ ). (Given : Specific heat capacity of water $= 4200\ \mathrm{J\,kg^{-1}\,{}^\circ C^{-1}}$ .)

15.

Questions 20 and 21 : The specific heat capacity of a metal is measured using the following method :

A metal block is first immersed in boiling water for some time. The block is then transferred to a cup of cold water. After a while, the temperature of the water is measured.

The result obtained in the last question is found to be higher than the true value of the specific heat capacity of the metal. Which of the following is a probable reason ?

16.

Graph of y against x: experimental points on a straight line with positive intercept y0 on the y axis

The above graph shows the result obtained when an experiment is performed to study the relation between the pressure and temperature of a fixed mass of gas at constant volume. Which of the following statements is/are correct ?

(1)The

y

- and

x

-axes denote the pressure and temperature of the gas respectively.

(2)The slope of the graph denotes the volume of the gas.

(3)The intercept

y_0

denotes the absolute zero temperature.

17.

A column of gas is trapped inside a cylinder. The piston is now pushed slowly causing the gas to be compressed at a constant temperature. Which of the following statements about the gas molecules in the cylinder is/are correct ?

(1)The average speed of the gas molecules increases.

(2)Each gas molecule exerts a greater impact force on the walls of the cylinder in each collision.

(3)The gas molecules collide more frequently with the walls of the cylinder.

18.

In a ripple tank experiment, a series of water waves travels towards a barrier. Which of the following quantities would remain unchanged after the waves are reflected by the barrier ?

(1)wavelength

(2)frequency

(3)speed

19.

A wave source generates waves of frequency $50$ Hz. How long does it take for the waves to travel $100$ m ?

20.

Ripple tank with spongy lining, plane water waves travelling towards an opening in a barrier

Which of the following phenomena would be observed when the water waves pass through the opening in the above set-up ?