物理 1996 年 DSE、CE 選擇題

1.

Which of the following expressions does not represent energy ?

2.

A man walks $40$ m towards the west. He then walks $40$ m towards the south and lastly walks $70$ m towards the east. Find the magnitude of the resultant displacement of the man.

3.

Which of the following statements about mass and weight is incorrect ?

4.

An object moves with uniform acceleration along a straight line. Which of the following graphs correctly describe(s) the motion of the object ?

Three graphs: (1) displacement-time curve rising with decreasing slope, (2) velocity-time straight line through the origin, (3) acceleration-time horizontal line

5.

Which of the following statements concerning the motion of an object is/are correct ?

(1)A constant unbalanced force is needed to keep an object moving with uniform velocity.

(2)An increasing unbalanced force is needed to keep an object moving with uniform acceleration.

(3)An object may remain at rest if there is no unbalanced force acting on it.

6.

Vacuum cylinder with a feather and a coin falling together

A coin and a feather are released from rest in a cylinder which is vacuum as shown. Which of the following is/are correct deductions from this experiment ?

(1)The masses of the coin and the feather are identical in vacuum.

(2)The coin and the feather fall with the same acceleration in vacuum.

(3)The forces acting on the coin and the feather in vacuum are identical.

7.

A motor car of mass $2500$ kg accelerates from rest to a speed of $20\ \mathrm{m\,s^{-1}}$ in $5$ s on a level road. Find the average power of the car.

8.

A block remains at rest on an inclined plane as shown above. Which of the following statements is/are true ?

(1)The frictional force acting by the plane on the block is zero.

(2)The normal reaction acting by the plane on the block is zero.

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

9.

Uniform plank AB resting on two trestles 1 m from each end and 3 m apart, weight 200 N at the middle, a boy standing at end B

A uniform plank $AB$ of weight $200$ N rests on two trestles as shown above. A boy stands at the end $B$ of the plank. What can be the maximum weight of the boy be without tilting the plank ? (Assume the weight of the plank acts through its centre.)

10.

The below diagram shows a man lifting a ball vertically upwards with uniform acceleration.

A hand lifting a ball upwards, with force arrows F1 upward on the ball, F2 and F3 downward

Let $F_1$ be the force acting on the ball by the man, $F_2$ be the force acting on the man by the ball, $F_3$ be the gravitational force acting on the ball. Which of the following correctly describes the relation between the magnitudes of the forces ?