物理 1981 年 DSE、CE 選擇題

1.

Masses m1 and m2 hung over a smooth pulley fixed to a ceiling

Two masses $m_1$ and $m_2$ ( $m_1 > m_2$ ) are hung over a smooth pulley as shown. If the system is released from rest, what is the kinetic energy of the system after the mass $m_1$ has descended through a distance $h$ ?

2.

A body of mass $M$ rests in equilibrium on a plane inclined at an angle $\theta$ to the horizontal. What is the frictional force acting on the body ?

Block M at rest on a plane inclined at angle theta

3.

A trolley of mass $1$ kg placed on a smooth horizontal table is connected by two light strings to blocks $A$ and $B$ of masses $0.75$ kg and $0.25$ kg respectively, as shown in the figure. $X$ and $Y$ are frictionless pulleys. When the system is released, what will be its acceleration ?

Trolley on a table connected over pulleys X and Y to hanging blocks A and B

4.

Five blocks A to E joined by strings S1 to S4, force F pulling A to the left on a smooth surface

Five blocks of equal mass $A$ , $B$ , $C$ , $D$ and $E$ are connected by four identical strings $S_1$ , $S_2$ , $S_3$ and $S_4$ as shown in the figure above. They are made to slide on a smooth horizontal surface by a steadily increasing force $F$ applied to block $A$ . Which of the strings is most likely to break first ?

5.

A vehicle moves up a road inclined at an angle $\theta$ to the horizontal with a constant velocity of $10\ \mathrm{m\,s^{-1}}$ . If the forces resisting the movement of the vehicle are uniform, the power developed by the vehicle engine is

6.

Which of the following statements concerning the motion of a body is/are correct ?

(1)A body has no acceleration when it is moving with a uniform velocity.

(2)A body can have zero velocity but also be accelerating.

(3)A body can have a constant speed but a varying velocity.

7.

A liquid placed inside an insulated vessel is kept boiling by a heating coil immersed in it. When the power supplied to the coil is $42$ W, the liquid boils away at a rate of $10^{-4}$ kg s $^{-1}$ . What is the specific latent heat of vaporization of the liquid ?

8.

$0.10$ g of steam at $100^\circ\mathrm{C}$ is mixed with $0.10$ g of ice at $0^\circ\mathrm{C}$ . No heat is lost to the surroundings. Which of the following describes the final mixture ? Given : specific heat capacity of water $= 4.2\ \mathrm{kJ\,kg^{-1}\,{}^\circ C^{-1}}$ specific latent heat of fusion of ice $= 336\ \mathrm{kJ\,kg^{-1}}$ specific latent heat of steam $= 2260\ \mathrm{kJ\,kg^{-1}}$

9.

An inexpansible vessel contains $1.2$ kg of a gas at $300$ K. What is the mass of gas expelled from the vessel if it is heated from $300$ K to $400$ K under constant pressure ?

10.

Ray falling on a convex lens with possible emergent rays P, Q, R and S; F is the principal focus

A ray of light falls on a convex lens as shown in the figure. $F$ is the principal focus of the lens. Which of the following represents the path of the emergent ray ?