物理 2010 年 DSE、CE 選擇題

1.

Mary walks along a triangular path $XYZ$ where $XY = YZ = ZX$ . It takes her $10$ s, $20$ s and $10$ s to travel through $XY$ , $YZ$ and $ZX$ respectively. Which of the following graphs best represents the variation of distance travelled with time ?

2.

Velocity-time graph rising linearly to a peak at t1 then falling linearly to zero

A man pushes a supermarket trolley with a constant horizontal force for $t_1$ seconds, and then releases the trolley. The velocity-time graph of the trolley is shown above. Assume that the friction between the trolley and the ground is constant, which of the following graphs (in dotted lines) best represents the variation of the velocity of the trolley with time if the man repeats the action with a stronger force ?

Four velocity-time graphs A to D, each with the original solid line and a dotted line

3.

Spring balance attached to a wall by a light string, horizontal force F pulling the balance

A spring balance is connected to the wall by a light string. A horizontal force $F$ is acting on the spring balance as shown below. The spring balance shows a reading of $5$ N. Assume that the mass of the balance can be neglected, what is the magnitude of the tension in the string ?

4.

A man is standing in a lift. The lift is initially at rest. When the lift starts to move upward, the man feels heavier. Which of the following statements is/are correct ?

(1)The gravitational force acting on the man increases.

(2)The gravitational force acting on the lift increases.

(3)The force acting on the man by the floor of the lift increases.

5.

Horizontal force F applied to a block on a smooth surface; graph of F against s rising linearly from 0 to 8 N at 2 m then constant to 5 m

Horizontal force $F$ is applied to a block of mass $4$ kg which is initially at rest on a horizontal smooth surface. The variation of the magnitude of $F$ with displacement $s$ is shown in the graph. The direction of $F$ remains unchanged throughout the motion. What is the work done on the block by $F$ from $s = 2$ m to $5$ m ?

6.

Questions 6 and 7 : A car is travelling along a straight horizontal path at $16\ \mathrm{m\,s^{-1}}$ initially. The driver sees an obstacle and applies the brake. The velocity-time graph of his car is shown below.

Velocity-time graph: constant 16 m/s until 1.2 s, then decreasing linearly to zero at 4.5 s

What is the magnitude of the deceleration of the car during braking ?

7.

Questions 6 and 7 : A car is travelling along a straight horizontal path at $16\ \mathrm{m\,s^{-1}}$ initially. The driver sees an obstacle and applies the brake. The velocity-time graph of his car is shown below.

Which of the following graphs best represents the variation of the kinetic energy (K.E.) of the car with distance $s$ travelled ?

Four graphs A to D of KE against distance s

8.

Three different solids, initially at $20^\circ\mathrm{C}$ , are heated at the same power.

Solid	Heat capacity / $\mathrm{J\,{}^\circ C^{-1}}$	Melting point / $^\circ$ C
$P$	300	218
$Q$	500	132
$R$	900	84

Which solid will start melting first ?

9.

Paper tray containing water heated from below by a flame

A paper tray contains some water. The tray is heated by a gentle flame from below as shown. The water in the tray starts to boil while the paper does not catch fire. Which of the following statements are correct in this situation ?

(1)Water can transfer heat away from the paper tray very quickly.

(2)Water remains at

100^\circ\mathrm{C}

when it is boiling.

(3)There is no heat transfer between the paper tray and the flame.

10.

People feel cooler when they get out of water after swimming. Which of the following is/are the reason(s) ?

(1)The water on the skin evaporates.

(2)The water on the skin absorbs latent heat of fusion.

(3)The water on the skin releases latent heat of vaporization.