物理 1997 年 DSE、CE 選擇題

1.

Which of the following expressions represents a physical quantity which is different from the others ?

2.

A student walks along a curve $ABC$ , which is made up of two semi-circular parts $AB$ and $BC$ of radius $3$ m and $4$ m respectively. He takes $2$ s to walk from $A$ to $B$ and $5$ s from $B$ to $C$ . Find the magnitude of the average velocity of the student from $A$ to $C$ .

Curve ABC made of two semi-circles AB (radius 3 m) and BC (radius 4 m) on opposite sides of the line AC

3.

A particle of mass $m$ is thrown vertically upwards with initial speed $v$ . When the particle returns to its starting point, what are the changes in momentum and kinetic energy of the particle ?

	Change in momentum	Change in kinetic energy
	$0$	$0$
	$0$	$mv^2$
	$2mv$	$0$
	$2mv$	$mv^2$

4.

A particle is released from rest and falls vertically under gravity. If the distance travelled by the particle in the 1st second is $x$ and that travelled in the 2nd second is $y$ , find the ratio $x : y$ .

5.

Pendulum bob released from A, with a fixed pin below the support on the vertical through B

A pendulum bob is suspended by a light inextensible string. The bob is released from rest at point $A$ . When the bob reaches the lowest point $B$ , the string hits a fixed pin. Neglect air resistance. Which of the following statements is/are correct ?

(1)The bob has maximum kinetic energy at

B

.

(2)The highest level that the bob can reach is the level of the pin.

(3)The work done by the tension of the string is zero throughout the motion.

6.

A machine lifts up a load of $1200$ N to a height of $1.5$ m in $2$ s. Find the average output power of the machine.

7.

Which of the following pairs of forces is/are action and reaction pair(s) according to Newton's third law of motion ?

(1)The weight of a man standing on a chair. and The force acting on the man by the chair.

(2)The gravitational force acting on the earth by the moon. and The gravitational force acting on the moon by the earth.

(3)The force exerted by a swimmer on the water to push the water backward. and The force exerted by the water to push the swimmer forward.

8.

Light plank on trestles S1 and S2: 0.25 m from the left end to S1, 1.25 m between the trestles, 0.5 m from S2 to the right end, with a boy at the mid-point

A light plank of length $2$ m rests on two trestles $S_1$ and $S_2$ as shown in the figure. A boy of weight $500$ N stands at the mid-point of the plank. Find the forces acting on the two trestles by the plank.

	Force acting on $S_1$	Force acting on $S_2$
	$166\frac23$ N	$333\frac13$ N
	$200$ N	$300$ N
	$250$ N	$250$ N
	$300$ N	$200$ N

9.

Object AB, its image A'B' and an optical device PQ with a ray from A passing through

In the above diagram, $A'B'$ is the image of an object $AB$ formed by an optical device $PQ$ . What is $PQ$ ?

10.

Which of the following phenomena involve(s) total internal reflection of light ?

(1)The sparkling of a diamond.

(2)The formation of a mirage.

(3)A ruler appearing bent when dipped in water.