物理 2009 年 DSE、CE 選擇題（第 4 頁）

31.

A tram of mass $1500$ kg is being pulled by a steel cable. It goes up a $30^\circ$ slope with a uniform speed. The average resistive force along the tram is $200$ N. What is the energy required for the tram to move $100$ m up along the slope ?

Tram pulled up a 30 degree slope by a cable

32.

An object is released from rest at the top of a building of height $h$ . At time $t_1$ , the object is at the half of the height of the building as shown in the figure. At time $t_2$ , the object just reaches the ground. Which of the following is/are correct ? (Neglect air resistance.)

(1)velocity of the object at

t_2 = 2\times

velocity of the object at

t_1

(2)

t_2 = 2\times t_1

(3)K.E. of the object at

t_2 = 2\times

K.E. of the object at

t_1

Building of height h with the object at t = 0 at the top, t = t1 at h/2 and t = t2 at the ground

33.

A bottle of $0.5$ kg water and a bottle of $0.75$ kg water have been stored in a refrigerator for a few days. Which of the following statements are correct ?

(1)The temperatures of the two bottles of water are equal.

(2)The average kinetic energy of the water molecules in the two bottles is equal.

(3)The total potential energy of the water molecules in the two bottles is equal.

34.

Three 45-90-45 triangular prisms X, Y and Z with a ray entering normally; the emergent rays differ

$X$ , $Y$ and $Z$ are three $45^\circ$ $-$ $90^\circ$ $-$ $45^\circ$ triangular prisms made of different transparent materials. A ray incident normally at one face is found to undergo refraction and reflection in each prism as shown in the figures above. Which of the following is the correct order of the refractive indices of the prisms ?

35.

Loudspeakers S1 and S2 connected to a signal generator, point X, O the mid-point of S1S2 and Y below X; not to scale

Sound waves of $660$ Hz are produced from two identical loudspeakers $S_1$ and $S_2$ which are connected in parallel to a signal generator. The distances $S_1X$ and $S_2X$ are $2$ m and $4$ m respectively. $O$ is the midpoint of $S_1S_2$ . What kinds of interference occur at $X$ and $Y$ respectively ? Given that the speed of sound in air is $330\ \mathrm{m\,s^{-1}}$

	$X$	$Y$
	constructive	constructive
	constructive	destructive
	destructive	constructive
	destructive	destructive

36.

Figure (a): particles a to k at equilibrium positions. Figure (b): positions at a certain instant

Figure (a) shows a series of particles ( $a$ - $k$ ) at their equilibrium positions. Figure (b) shows the positions of the particles at a certain instant when a longitudinal wave travels to the right passes through the particles. Which are the directions of the motion of particles $c$ and $f$ at the instant shown in Figure (b) ?

	Particle $c$	Particle $f$
	to left	to left
	to left	to right
	to right	to left
	to right	to right

37.

A musical note is produced by a guitar string. Which of the following properties about the sound wave produced and the wave in the string is/are the same ?

(1)wavelength

(2)frequency

(3)wave speed

38.

Circular wavefronts from two identical dot vibrators S1 and S2 with a point P marked

The figure above shows the circular wavefronts produced by two identical dot vibrators, $S_1$ and $S_2$ , in a ripple tank at time $t=0$ . Solid lines represent crests. A cork is placed at point $P$ on the water surface. Which of the following graphs best represents the variation of the displacement $s$ of the cork with time $t$ ? (Take upward as the positive direction.)

39.

Bar magnet with ends X and Y moving left towards a solenoid with ends P and Q, dashed outline showing the earlier position, solenoid connected to a resistor

When a magnet is moving towards end $Q$ for a solenoid, it is found that a north pole is induced at end $Q$ . As shown in the figure above, the magnet passes through and moves away from the solenoid, what are the polarities of end $P$ of the solenoid and end $X$ of the magnet ?

	Polarity of end $P$	Polarity of end $X$
	S	S
	S	N
	N	S
	N	N

40.

Generator: coil between S and N poles with slip rings, brushes and a load PQ

The figure above shows the position of the coil in a generator at time $t=0$ . The current is taken to be positive when it flows from $P$ to $Q$ through the load. Which of the following graphs best represents the variation of current $I$ with time $t$ as the coil rotates ?