物理 1984 年 DSE、CE 選擇題

1.

If the engine of a rocket travelling in space is turned off, the rocket will

2.

The diagram shows how the velocity of a body varies with time. What is the distance travelled in the first $4$ s ?

Velocity-time graph: straight line from 2 m/s at t = 0 to 4 m/s at t = 4 s

3.

Which of the following velocity-time graphs correctly shows the motion of a ping-pong ball falling freely in a vacuum ?

Four velocity-time graphs A to D: A straight line falling from a positive value to zero; B straight line through the origin; C curve rising and levelling off; D curve falling and levelling off

4.

A basketball falls freely from rest and hits the ground. It then rebounds to $1/4$ of its original height. Neglecting air resistance, which of the following statements about the basketball is/are correct ?

(1)Its kinetic energy just before collision is four times its kinetic energy just after collision.

(2)Its potential energy just before collision is four times its potential energy just after collision.

(3)The speed just before collision is two times the speed just after collision.

5.

A cannon ball is fired so that it hits the wall at the top of a $10$ m tower. If the energy needed to destroy the wall is $49000$ J and the mass of the cannon ball is $10$ kg, the minimum initial velocity of the cannon ball required to break the tower wall is

6.

A bullet hits a target at a speed of $200\ \mathrm{m\,s^{-1}}$ . If $50\%$ of the kinetic energy has been converted into the internal energy of the bullet, what is the rise in temperature of the bullet ? (Specific heat capacity of the bullet $= 100\ \mathrm{J\,kg^{-1}\,{}^\circ C^{-1}}$ )

7.

If an immersion heater takes $10$ minutes to bring a cup of water to its boiling point $100^\circ\mathrm{C}$ from the room temperature of $20^\circ\mathrm{C}$ , what will be the time taken for the boiling water to vaporize completely ? (Specific heat capacity of water $= 4.2\ \mathrm{kJ\,kg^{-1}\,{}^\circ C^{-1}}$ ; specific latent heat of steam $= 2268\ \mathrm{kJ\,kg^{-1}}$ .)

8.

Cooling curve of liquid naphthalene: temperature falls from A (80 degrees C) to B, stays at about 70 degrees C between B and C, then falls to D

A cooling curve for liquid naphthalene is shown above. From the graph, which of the following statement(s) is/are true ?

(1)The melting point of naphthalene is around

70^\circ\mathrm{C}

.

(2)In the period

BC

, only liquid naphthalene is present.

(3)In the period

BC

, no energy is given by naphthalene to the surroundings.

9.

An immersion heater of resistance $50\ \Omega$ raises the temperature of $1$ kg of water by $20^\circ$ C in $3$ minutes, the voltage supply being $200$ V. What would be the energy wasted ? (Specific heat capacity of water $= 4.2\ \mathrm{kJ\,kg^{-1}\,{}^\circ C^{-1}}$ )

10.

An equal quantity of heat is supplied to each of the following substances and the corresponding rises in temperature are recorded. Which of the following substances has the smallest specific heat capacity ?

Substance	Mass (kg)	Rise in temperature ( $^\circ$ C)
$P$	2.5	5
$Q$	3.0	4
$R$	4.5	3
$S$	5.0	3