物理 2006 年 DSE、CE 選擇題

1.

Velocity-time graphs of cars A (steep then shallow, solid) and B (shallow then steep, dashed) meeting at time T

Two cars $A$ and $B$ start from rest simultaneously and travel along the same straight road. The velocity-time graphs of the two cars are shown above. Which of the following statements about the motion of the two cars is/are always correct ?

(1)

A

and

B

have the same average velocity during the time interval

0

to

T

.

(2)

A

and

B

have the same average acceleration during the time interval

0

to

T

.

(3)

A

and

B

travel the same displacement during the time interval

0

to

T

.

2.

Many traffic accidents on highways are associated with inertia. Which of the following traffic regulations can reduce the risk of traffic accidents due to inertia ?

(1)Passengers should wear seat belts.

(2)Vehicles should not be overloaded.

(3)People should not drive over the speed limit.

3.

Marble at the top of a table with two smooth rails A (steeper) and B (gentler) down to the ground

John releases a marble from the top of a smooth rail $A$ placed at the edge of a table as shown above. He repeats the same process by using another smooth rail $B$ . Which of the following statements about the marble is/are correct ?

(1)The marble has the same velocity when it reaches the ends of both rails.

(2)The marble has the same kinetic energy when it reaches the ends of both rails.

(3)It takes the same time for the marble to travel through both rails.

4.

A car stopped after emergency braking. The skid mark left by the car was $22.3$ m long. Assume that the friction between the road and tyres was $0.65$ times that of the weight of the car. Estimate the speed of the car when it began to skid.

5.

A high-diver jumps up into the air from a spring board and then falls into a swimming pool. Which of the following graphs best shows the variation of her kinetic energy $K$ with time $t$ from the time she just leaves the board up to the moment just before she enters the water ? (Neglect air resistance.)

Four graphs A to D of kinetic energy K against time t

6.

An electric fan is installed at one end of a trolley and a card is fixed at the other end with the plane of the card facing the fan. What happens to the trolley when the electric fan is turned on ?

Trolley with an electric fan at the right end and a card at the left end; air flow arrow pointing left; trolley on the ground

7.

The acceleration of objects due to gravity on the Moon is about $1/6$ that on the Earth. Which of the following diagrams shows the correct velocity-time graphs for a free falling object dropping respectively on the Earth's surface and the Moon's surface ?

Four velocity-time diagrams A to D each showing lines for Earth and Moon

8.

Peter standing on a weighing scale and pressing down on a table with his hands with force F

If Peter stands with his feet on a weighing scale placed on level ground, his weight measured by the scale is $W$ . What would be the reading on the scale if he exerts a downward force $F$ on a table top with his hands while he is still standing on the same scale as shown above ?

9.

Vacuum flask with cork stopper, hot liquid, double glass walls with vacuum between, and surfaces P and Q

The figure shows a vacuum flask with two glass walls. Which of the following statements are correct ?

(1)The surfaces

P

and

Q

are painted silvery to reduce heat loss.

(2)The cork stopper reduces heat loss by conduction and convection.

(3)The vacuum between the double glass walls reduces heat loss by radiation.

10.

A space shuttle is covered by 'heat shields' over its body so as to protect the interior from getting too hot while entering the atmosphere of the Earth. Which of the following thermal properties is/are desirable for the material of the 'heat shields' ?

(1)It should be a good conductor of heat.

(2)It should have a very high melting point.

(3)It should have high specific heat capacity.