物理 1988 年 DSE、CE 選擇題

1.

Stroboscopic photograph of a ball rolling down a slope with positions K, L, M, N, O, P at 0, 4, 16, 36, 64 and 100 cm

The above figure shows the stroboscopic photograph of a ball rolling down a slope. If the stroboscope makes $2$ flashes per second, in which region does the ball have an average speed of $40$ cm s $^{-1}$ ?

2.

The figure shows two trolleys moving towards each other along a smooth runway. After collision, they stick together. What is the total loss in kinetic energy by the trolleys during the collision ?

A 2 kg trolley moving right at 4 m/s and a 1 kg trolley moving left at 2 m/s on a smooth runway

3.

The figure shows a trolley of mass $1$ kg being released from rest from point $X$ of a rough slope. Its speed at $Y$ is $3\ \mathrm{m\,s^{-1}}$ . What is the loss in energy by the trolley when it is moving from $X$ to $Y$ ? (Take $g = 10\ \mathrm{m\,s^{-2}}$ .)

Trolley at X on a rough slope, 1 m above the level of Y

4.

Mass M on a smooth table connected over a pulley to hanging mass m

The figure above shows a mass $m$ connected to another mass $M$ by a string passing over a smooth pulley. The system is moving freely under gravity. Assuming that the table is smooth, which of the following statements is/are correct ?

(1)

m

and

M

move with the same acceleration in magnitude.

(2)The loss in potential energy of

m

is equal to the gain in kinetic energy of

M

.

(3)If the mass of

M

is doubled, its acceleration is halved.

5.

The figure shows a smooth inclined plane with $Y$ being midway between $XZ$ . Two particles $A$ and $B$ of the same mass are released from rest at $X$ and $Y$ respectively. Which of the following statements about $A$ and $B$ is/are true ?

(1)The time required for

A

to reach

Z

is double that for

B

to reach

Z

.

(2)The potential energy for

A

at

Z

is double that for

B

at

Z

.

(3)The kinetic energy for

A

at

Z

is double that for

B

at

Z

.

Smooth inclined plane XZ with particle A at X and particle B at the midpoint Y

6.

The pressure exerted by a gas in a container would increase if

(1)the average speed of the gas molecules were increased.

(2)the number of gas molecules were increased.

(3)the volume of the container were increased.

7.

Five different solids, each of mass $1$ kg, are heated by identical immersion heaters for $10$ minutes. The following graphs show their heating curves. Assuming no loss in heat, which solid has the greatest specific latent heat of fusion ?

Four temperature-time heating curves A to D over 0 to 10 min, each with a horizontal melting section of different length

8.

Object O, image I and points P, Q, R, S on the axis of a concave lens

The figure shows an object $O$ placed in front of a concave lens to give an image $I$ . What is the most probable position of the focus ?

9.

In a ripple tank, when water waves pass through a narrow gap in a barrier, what happens to its frequency and wavelength ?

	Frequency	Wavelength
	increases	decreases
	decreases	increases
	decreases	remains unchanged
	remains unchanged	remains unchanged

10.

The range of sound that a boy can hear is from $30$ Hz to $16500$ Hz. If it is given that the speed of sound in air is $330\ \mathrm{m\,s^{-1}}$ , what is the shortest wavelength of sound in air that the boy can hear ?