物理 2001 年 DSE、CE 選擇題（第 2 頁）

11.

A rocket of mass $5000$ kg is at rest in space. It then explodes and breaks into two parts $P_1$ and $P_2$ of mass $1000$ kg and $4000$ kg respectively. Find the ratio of the kinetic energy of $P_1$ to $P_2$ .

12.

A melting ice block of mass $0.05$ kg is mixed with $x$ kg of water at $0^\circ\mathrm{C}$ in a well-insulated container. If $25\,000$ J of energy is supplied to the mixture, the mixture changes to water at $4^\circ\mathrm{C}$ . Find the value of $x$ . (Given : specific latent heat of fusion of ice $= 3.34\times10^5\ \mathrm{J\,kg^{-1}}$ , specific heat capacity of water $= 4200\ \mathrm{J\,kg^{-1}\,{}^\circ C^{-1}}$ .)

13.

Copper block on a polystyrene plate with an immersion heater, thermometer and joulemeter

The apparatus shown is used to measure the specific heat capacity of a cylindrical copper block. The result of the experiment is as follows : Mass of copper block $= m$ kg Initial temperature $= 21^\circ\mathrm{C}$ Final temperature $= 47^\circ\mathrm{C}$ Initial joulemeter reading $= R_1$ J Final joulemeter reading $= R_2$ J Which of the following expressions gives the specific heat capacity of copper in $\mathrm{J\,kg^{-1}\,{}^\circ C^{-1}}$ ?

14.

The figure shows the cooling curve of a substance which is initially in the liquid state. The temperature of the substance remains unchanged during the period $PQ$ . Which of the following statements about the substance during the period $PQ$ is/are correct ?

(1)The substance is not losing any energy to the surroundings.

(2)Latent heat is absorbed by the substance.

(3)The average potential energy of the molecules of the substance is decreasing.

Cooling curve of temperature against time with a flat section between points P and Q

15.

Flask of gas heated by a burner in a beaker of water with stirrer and thermometer, connected by rubber tubing to a Bourdon gauge

The above apparatus is used to study the relation between pressure and temperature of a fixed mass of gas at constant volume. Which of the following can improve the accuracy of the experiment ?

(1)using a larger flask

(2)using a shorter length of rubber tubing to connect the gauge and the flask

(3)setting up a control experiment with the burner removed

16.

The graph shows the $V$ - $T$ relation of a fixed mass of ideal gas. Point $X$ denotes the initial state of the gas. The gas changes its state from $X$ to $Y$ , then from $Y$ to $Z$ and finally from $Z$ back to $X$ along the path shown. Which of the following statements about the pressure of the gas is/are correct ?

(1)The pressure remains unchanged in the transition from

X

to

Y

.

(2)The pressure increases in the transition from

Y

to

Z

.

(3)The pressure decreases in the transition from

Z

to

X

.

V against T graph: X to Y along a straight line towards the upper right, Y to Z vertically down, Z to X horizontally

17.

Which of the following is **not** a transverse wave ?

18.

Water wave moving to the left with corks P, Q, R and S on the surface

Four corks are moving up and down on the surface of a pond as a water wave passes through them. At time $t=0$ , the positions of the corks are shown above. The figure below shows the displacement-time graph of one of the four corks. (Note : Displacement is positive when the cork is above the still water surface.)

Displacement against time graph starting at zero and rising first

Which cork has the motion represented by the graph ?

19.

A sonar on a ship is used to find the depth of the sea. An ultrasonic wave pulse is sent downwards from the ship towards the sea bed. The pulse travels with a speed of $1500\ \mathrm{m\,s^{-1}}$ in sea water. If the reflected pulse is received after $0.16$ s, find depth of the sea.

20.

Boundary XY between a deep region and a shallow region with straight waves approaching obliquely from the deep region

In the above diagram, $XY$ represents a boundary between a deep region and a shallow region of water in a ripple tank. A series of straight water waves in the deep region travels towards $XY$ . Which of the following diagrams best shows the wave pattern in the shallow region ?

$Four refraction diagrams A to D$