物理 2004 年 DSE、CE 選擇題

1.

Three displacement-time graphs: car P (straight line), car Q (curve flattening), car R (curve steepening)

Three cars $P$ , $Q$ and $R$ move along a straight horizontal road. Their displacement-time graphs are shown above. Which of the cars experience a change in momentum during the motion ?

2.

An object weighs $60$ N on the Earth and $10$ N on the moon. Which of the following statements are correct ? (Take the acceleration due to gravity to be $10\ \mathrm{m\,s^{-2}}$ .)

(1)The mass of the object on the Earth is

6

kg.

(2)The mass of the object on the moon is

1

kg.

(3)The acceleration due to gravity on the moon is one-sixth that on the Earth.

3.

Velocity-time graphs of P (steep line stopping at a constant value) and Q (straight line of smaller slope) from the origin, with t1 and t2 marked

The figure shows the velocity-time graphs of two students $P$ and $Q$ running along a straight road. They start at the same point. Which of the following statements is/are correct ?

(1)The average speed of

P

between

t = 0

and

t = t_1

is larger than that of

Q

.

(2)At

t = t_1

,

P

and

Q

reach the same point.

(3)At

t = t_2

,

Q

is ahead of

P

.

4.

An object is acted on by three forces $F_1$ , $F_2$ and $F_3$ in suitable directions such that it remains at rest. Which of the following combinations of the magnitudes of the forces is/are possible ?

	$F_1$	$F_2$	$F_3$
(1)	$3$ N	$4$ N	$5$ N
(2)	$3$ N	$4$ N	$7$ N
(3)	$3$ N	$5$ N	$9$ N

5.

Figure (a): masses m1 and m2 joined by a string with tension T1, force F pulling m2 to the right. Figure (b): force F pulling m1 to the left, tension T2

Two blocks, of masses $m_1$ and $m_2$ $(m_1>m_2)$ , are connected by a light inextensible string and placed on a smooth horizontal surface. Let $T_1$ and $T_2$ be the tensions in the string when a horizontal force $F$ is applied to the blocks as shown in Figures (a) and (b) respectively. Which of the following relationships are correct ?

(1)

T_1>T_2

(2)

\dfrac{T_1}{m_1}=\dfrac{T_2}{m_2}

(3)

T_1+T_2=F

6.

Graph of y against x: a straight line through the origin

A block is initially at rest on a smooth horizontal surface and is pulled by a constant horizontal force. The figure shows the relationship between the physical quantities $y$ and $x$ . Which of the following combinations of $y$ and $x$ is impossible ?

	$y$	$x$
	displacement of the block	square of time
	velocity of the block	time
	square of velocity of the block	displacement of the block
	acceleration of the block	time

7.

Photograph of a sucker sticking to a hook on a vertical wall

The photograph shows a sucker sticking to a hook on a vertical wall. Which of the following forces balances the gravitational force acting on the sucker and hook by the Earth ?

8.

A trolley moves along a smooth horizontal surface. A lump of plasticine is released from a height slightly above the trolley and sticks to it. Which of the following graphs shows the variation of the total horizontal momentum $p$ of the trolley and plasticine with time $t$ ?

Four graphs A to D of total horizontal momentum p against time t

9.

Photograph of an air-cushioned shoe with the air-cushion labelled

The photograph shows an air-cushioned shoe. Which of the following statements about the air-cushion is/are correct ?

(1)It reduces the time of impact between the foot and the ground during running.

(2)It reduces the impact force acting on the foot during running.

(3)It reduces the friction between the shoe and the ground during running.

10.

Figure (a): uniform plank, 1 m long, hung by two spring balances P and Q at its ends. Figure (b): balance P moved 0.25 m towards Q

Figure (a) shows a uniform plank supported by two spring balances $P$ and $Q$ . The readings of the two balances are both $150$ N. $P$ is now moved $0.25$ m towards $Q$ (see Figure (b)). Find the new readings of $P$ and $Q$ .

	Reading of $P$ / N	Reading of $Q$ / N
	$100$ N	$200$ N
	$150$ N	$150$ N
	$200$ N	$100$ N
	$200$ N	$150$ N