物理 1995 年 DSE、CE 選擇題

1.

Which of the following pairs of physical quantities has the same units ?

2.

A 4 kg block and a 2 kg block joined by string S on a smooth surface, force F pulling the 2 kg block to the right

Two blocks are connected together by a light string $S$ placed on a smooth horizontal surface. They move with uniform acceleration of $2\ \mathrm{m\,s^{-2}}$ under the action of force $F$ . What will the accelerations of the blocks become if $S$ suddenly breaks ?

	$2$ kg block	$4$ kg block
	$6\ \mathrm{m\,s^{-2}}$	$0\ \mathrm{m\,s^{-2}}$
	$6\ \mathrm{m\,s^{-2}}$	$2\ \mathrm{m\,s^{-2}}$
	$2\ \mathrm{m\,s^{-2}}$	$0\ \mathrm{m\,s^{-2}}$
	$0\ \mathrm{m\,s^{-2}}$	$3\ \mathrm{m\,s^{-2}}$

3.

A stone is thrown vertically upwards and it finally falls back to the starting point. Assume air resistance is negligible. Which of the following statements is/are true throughout the motion ?

(1)The acceleration of the stone is constant.

(2)The total mechanical energy of the stone is conserved.

(3)The momentum of the stone is conserved.

4.

An object starts from rest and moves with uniform acceleration along a straight line. Which of the graphs below concerning the motion of the object is/are correct ? ( $s$ = displacement, $v$ = velocity, $t$ = time)

Three graphs: (1) v against t, (2) s against t squared, (3) v squared against s, each a straight line through the origin

5.

Two objects of different masses are released from rest at the same height. Assume air resistance is negligible. Which of the following statements is/are correct ?

(1)A greater gravitational force is acting on the object with greater mass.

(2)They take the same time to reach the ground.

(3)They have equal velocities when they reach the ground.

6.

A trolley is placed on a horizontal ground. A force $F$ inclined at an angle $\theta$ to the horizontal acts on the trolley. What is the horizontal component of $F$ that pulls the trolley towards the right ?

Trolley pulled by force F at angle theta above the horizontal

7.

A car moves with a speed $30$ km h $^{-1}$ . The driver applies the brake and the car is stopped in a distance of $12$ m. If the car is moving at $60$ km h $^{-1}$ , what is the stopping distance ? Assume that the same constant braking force is applied in both cases.

8.

Velocity-time graph: straight line from 20 m/s at t = 0 through zero at 2 s to -10 m/s at 3 s

The above diagram shows the variation of the velocity of an object with time. What is the distance travelled by the object in the first $3$ seconds ?

9.

Figure (a): bullet at 450 m/s passing through a single wooden block. Figure (b): bullet at 450 m/s approaching a stack of identical blocks

A bullet of mass $0.02$ kg traveling at $450\ \mathrm{m\,s^{-1}}$ enters a wooden block as shown in Figure (a) and leaves it with a speed $400\ \mathrm{m\,s^{-1}}$ . In figure (b), what is the maximum number of identical blocks that the same bullet can pass through ?

10.

A trolley runs down a friction-compensated runway as shown above. Which of the following statements is true ?