物理動量 DSE、CE 選擇題（第 3 頁）

21.

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

22.

A particle of mass $m$ is thrown vertically upwards with initial speed $v$ . When the particle returns to its starting point, what are the changes in momentum and kinetic energy of the particle ?

	Change in momentum	Change in kinetic energy
	$0$	$0$
	$0$	$mv^2$
	$2mv$	$0$
	$2mv$	$mv^2$

23.

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.

24.

Which of the following pairs of physical quantities has/have the same unit ?

(1)Work and potential energy

(2)Power and momentum

(3)Specific heat capacity and specific latent heat of fusion

25.

A trolley of mass $2$ kg moves with a uniform speed of $4\ \mathrm{m\,s^{-1}}$ along a horizontal table. A lump of plasticine having the same mass as the trolley is dropped from a height slightly above the trolley and sticks to it. Find the total loss in kinetic energy.

Lump of plasticine above a trolley on a horizontal table

26.

A ball collides with a fixed wall and bounces back with the same speed. Which of the following quantities of the ball remain(s) unchanged before and after the collision ?

(1)kinetic energy

(2)velocity

(3)momentum

27.

Two particles $A$ and $B$ of masses $2$ kg and $1$ kg respectively move in opposite directions. The initial velocity of $A$ is $4\ \mathrm{m\,s^{-1}}$ towards the right, while that of $B$ is $2\ \mathrm{m\,s^{-1}}$ towards the left. They collide head on. After the collision, the velocity of $A$ becomes $1\ \mathrm{m\,s^{-1}}$ towards the right. What would be the velocity of particle $B$ ?

Particle A moving right at 4 m/s and particle B moving left at 2 m/s

28.

Ticker-tape timer, trolley moving along a horizontal surface and a lump of plasticine above it

A trolley moves with constant speed along a horizontal surface. A lump of plasticine having the same mass as the trolley is dropped onto the trolley and sticks to it. Which one of the following ticker-tape best represents the motion of the trolley ?

Four ticker-tapes A to D with printed dots

29.

Which of the following statements is/are correct when a collision between two particles is elastic ?

(1)None of the original kinetic energy is converted into other forms of energy.

(2)The linear momentum of each particle is conserved.

(3)The mechanical energy of each particle is conserved.

30.

A small metal ball is released from a point above the floor and bounces several times. Which of the following graphs best represents the variation of the velocity of the ball with time ?

Four graphs A to D of velocity v against time t