物理 1985 年 DSE、CE 選擇題

1.

Velocity-time graph: straight line from the origin to 6 m/s at t = 3 s

The graph shows the variation of the velocity of a car with time. What is the acceleration of the car ?

2.

A car moving with speed $50$ km h $^{-1}$ can be stopped in a distance of $15$ m. In what distance can the car be stopped when its speed is $70$ km h $^{-1}$ under the same condition ?

3.

Graph I: speed against time with a shaded triangle under the line. Graph II: force against distance with a shaded triangle under the line

What physical quantity does the area of the shaded portion of each of the above graphs represent ?

	I	II
	acceleration	energy
	distance	power
	acceleration	change of momentum
	distance	energy

4.

A ball of mass $2$ kg drops from rest to the ground from a height $5$ m and rebounds to the same height. If the time of duration of the impact between the ball and the ground is $0.2$ s, what is the force acting on the ball by the ground ? (Take the acceleration due to gravity be $10\ \mathrm{m\,s^{-2}}$ )

5.

An object is projected vertically upwards. Which of the graphs below correctly describes the variation of the kinetic energy $E$ of the object with height $h$ ?

Four graphs A to D of kinetic energy E against height h

6.

Hand pulling with a 10 N spring balance, string T1 to block A, string T2 to block B on a smooth surface

Two blocks $A$ and $B$ of masses $1$ kg and $1.5$ kg respectively are resting on a smooth horizontal surface and are linked by a string. They are pulled by a force of $10$ N as shown in the diagram. What are the tensions $T_1$ and $T_2$ ?

	Tension $T_1$	Tension $T_2$
	$10$ N	$10$ N
	$10$ N	$6$ N
	$10$ N	$4$ N
	$6$ N	$4$ N

7.

A block is moving with uniform velocity along a rough horizontal plane. Which of the following statements is/are true ?

(1)The kinetic energy of the block is increasing.

(2)The potential energy of the block is increasing.

(3)The resultant force acting on the block is zero.

8.

A diver jumps up at $A$ from a high platform into water at the point $B$ as shown. The diver descends to $C$ and then floats up to the water surface. Assume that the potential energy at point $B$ is taken to be zero. Which of the following statements is/are true concerning the diver at point $C$ ?

(1)The kinetic energy of the diver is at a maximum.

(2)The kinetic energy of the diver is at a minimum.

(3)The sum of the kinetic energy and potential energy of the diver is zero.

Diver path from platform A, down through water surface B to the lowest point C

9.

Block given an initial velocity up a smooth inclined plane

A block is given an initial velocity up a smooth inclined plane. Which graph below shows the acceleration of the block against time ? (The upward direction of motion along the plane is taken as positive.)

10.

The initial pressure of a fixed mass of gas at $25^\circ$ C is $2\times10^5$ Pa. What would its pressure be if the gas were reduced to half of its original volume and its temperature were increased to $95^\circ$ C ?