物理牛頓運動定律 DSE、CE 選擇題（第 7 頁）

61.

Block sliding down a friction-compensated runway

A block is sliding down a friction compensated runway as shown. Which of the following statements is/are correct ?

(1)The speed of the block is increasing.

(2)The normal reaction acting by the runway on the block is increasing.

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

62.

A light rope is fixed at two poles with the ends $A$ and $B$ at the same level. A T-shirt of weight $2$ N is hung at the midpoint $C$ of the rope. The rope depresses such that $\angle ACB = 150^\circ$ . Find the tension in the rope.

T-shirt hung from the midpoint C of a rope tied between poles A and B, angle ACB 150 degrees

63.

A broken-down car of mass $1000$ kg is pulled by a tow-truck and moves at a constant velocity $8\ \mathrm{m\,s^{-1}}$ along a horizontal road. It is known that the frictional force acting on the car is $500$ N. Find the tension in the cable connecting the truck and the car.

A tow-truck pulling a broken-down car to the right at 8 m/s

64.

Grid showing forces F1 and F2 acting on a particle P; scale 1 cm represents 1 N

Two forces $F_1$ and $F_2$ act on a particle $P$ as shown. If a third force $F_3$ acts on $P$ to keep it in equilibrium, what should be the magnitude of $F_3$ ?

65.

A girl in a lift uses a spring balance to measure the weight of an object. The reading of the spring balance is $10$ N when the lift is at rest. When the lift is moving, the reading of the spring balance becomes $8$ N. Which of the following describes the motion of the lift ?

66.

Which of the following phenomena can be explained by Newton's first law of motion ?

(1)A passenger in a car tends to move forward when the car suddenly stops.

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

(3)The maximum mass an astronaut can lift on the moon is greater than on earth.

67.

Which of the following pairs of forces is/are action and reaction pair(s) according to Newton's third law of motion ?

(1)The weight of a man standing on a chair. and The force acting on the man by the chair.

(2)The gravitational force acting on the earth by the moon. and The gravitational force acting on the moon by the earth.

(3)The force exerted by a swimmer on the water to push the water backward. and The force exerted by the water to push the swimmer forward.

68.

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

69.

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.

70.

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.