物理 2008 年 DSE、CE 選擇題

1.

A fish jumps up vertically to a maximum height of $0.5$ m above the water surface. What is the speed when it just leaves the surface ?

2.

A car is travelling at a constant speed of $15\ \mathrm{m\,s^{-1}}$ along a horizontal straight road. The total resisting force acting on the car is $500$ N. Which of the following statements are correct ?

(1)The car travels a distance

120

m in

8

s.

(2)The work done by the car in overcoming the resisting force in

8

s is

60

kJ.

(3)The output power of the car is

7.5

kW.

3.

Velocity-time graph of a car: rises slightly to t1, constant until t1, then falls linearly to zero

The figure above shows the velocity - time graph of a car travelling on a horizontal straight road. Which of the following statements is/are correct ?

(1)Area under the graph is equal to the total displacement of the car.

(2)The acceleration of the car is maximum at time

t_1

.

(3)The kinetic energy of the car remains unchanged throughout the whole journey.

4.

Blocks A and B joined by a string on a smooth surface, 10 N force pulling A to the left and 4 N force pulling B to the right

Two blocks $A$ and $B$ of the same mass on a smooth horizontal surface are connected by a string as shown above. Two horizontal forces of $10$ N and $4$ N are acting on $A$ and $B$ respectively. Assume all contact surfaces are smooth. What is the magnitude of the tension in the string ?

5.

Velocity-time graphs of a car (straight line from the origin to 20 m/s at 20 s) and a truck (constant 10 m/s)

At $t = 0$ , a car and a truck are at the same point on a horizontal straight road. Their velocity - time graph is shown in the figure above. Which of the following statements is correct ?

6.

Figure (a): a block on a table on the ground. Figure (b): forces F3 and F1 on the block and F2 on the table

A block is placed on a table resting on the ground as shown in Figure (a) above. Figure (b) shows the forces acting on the block and the table respectively.

Let $F_1$ = weight of the block

$F_2$ = force exerted by the block on the table

$F_3$ = force exerted by the table on the block

Which of the following statements are correct ?

(1)

F_1

and

F_2

represent the same force.

(2)

F_1

and

F_3

balance each other.

(3)

F_2

and

F_3

form an action-reaction pair.

7.

An object is released from rest. Which of the following graphs best describes the variation of the kinetic energy of the object with time during falling ? (Neglect air resistance.)

8.

Photograph of an aluminium heat sink with fins

The above figure shows the aluminium heat sink of an audio amplifier which is used to transfer heat away from the components inside the amplifier. Which of the following statements about the heat sink is/are correct ?

(1)The heat sink is made of aluminium so that it can transfer heat away faster by conduction.

(2)The heat sink is silver in colour so that it can transfer heat away faster by radiation.

(3)The heat sink has a fin-like design to increase the surface area so that it can transfer heat away faster by conduction to air.

9.

A $100$ W immersion heater is used to heat $0.5$ kg of water, which is being stirred by a stirrer. After $3$ minutes, the water temperature increases from $25^\circ\mathrm{C}$ to $30^\circ\mathrm{C}$ . What is the estimated energy loss in this period ? Given : specific heat capacity of water $= 4200\ \mathrm{J\,kg^{-1}\,{}^\circ C^{-1}}$

Beaker of water with thermometer, stirrer and immersion heater

10.

Which of the following statements is/are correct ?

(1)Energy transfers from an object with higher internal energy to an object with lower internal energy.

(2)An object must absorb energy when it changes its state.

(3)Energy transfers from an object with higher temperature to an object with lower temperature.