物理 1998 年 DSE、CE 選擇題

1.

Which of the following units does not represent energy ?

2.

A car undergoes uniform deceleration along a straight road. Its velocity decreases from $30$ m s $^{-1}$ to $20$ m s $^{-1}$ after travelling a distance of $100$ m. How much further will the car travel before it comes to a rest ?

3.

A block is pulled by a constant force and moves along a smooth horizontal surface. Which of the following describes the variations of the acceleration and momentum of the block during the time when the force is acting ?

	Acceleration	Momentum
	remains unchanged	remains unchanged
	remains unchanged	increases
	increases	remains unchanged
	increases	increases

4.

Velocity-time graph: rises from zero to 10 s, constant until 30 s, then decreases through zero at about 35 s to negative values by 40 s

The velocity-time graph of a car travelling along a straight horizontal road is shown above. Which of the following graphs shows the variation of the acceleration $a$ of the car with the time $t$ ?

5.

At time $t = 0$ , a table-tennis ball is released from a point above the ground and bounces several times on the ground. The graph shows the variation of the velocity $v$ of the ball with time $t$ . At which of the following points on the graph does the ball reach its maximum height above the ground after the first rebound ? (Note : Velocity pointing upwards is taken to be positive.)

Velocity-time graph of a bouncing ball with labelled points P, Q, R and S

6.

A broken-down car of mass $1000$ kg is pulled by a tow-truck and moves at a constant velocity $8\ \mathrm{m\,s^{-1}}$ along a horizontal road. It is known that the frictional force acting on the car is $500$ N. Find the tension in the cable connecting the truck and the car.

A tow-truck pulling a broken-down car to the right at 8 m/s

7.

Grid showing forces F1 and F2 acting on a particle P; scale 1 cm represents 1 N

Two forces $F_1$ and $F_2$ act on a particle $P$ as shown. If a third force $F_3$ acts on $P$ to keep it in equilibrium, what should be the magnitude of $F_3$ ?

8.

A girl in a lift uses a spring balance to measure the weight of an object. The reading of the spring balance is $10$ N when the lift is at rest. When the lift is moving, the reading of the spring balance becomes $8$ N. Which of the following describes the motion of the lift ?

9.

Which of the following phenomena can be explained by Newton's first law of motion ?

(1)A passenger in a car tends to move forward when the car suddenly stops.

(2)A coin and a feather fall with the same acceleration in a vacuum.

(3)The maximum mass an astronaut can lift on the moon is greater than on earth.

10.

A smooth inclined plane makes an angle $30^\circ$ with the horizontal as shown. A man pulls a $50$ kg block up the inclined plane with uniform velocity. The inclined plane is $6$ m long and the block is pulled from the bottom of the inclined plane to the top in $30$ s. Find the average power of the man. Take the acceleration due to gravity to be $10\ \mathrm{m\,s^{-2}}$ .

50 kg block on a smooth incline of 30 degrees, 6 m long