物理位置與運動 DSE、CE 選擇題（第 5 頁）

41.

An object is falling from rest with an acceleration of $9.8$ m s $^{-2}$ . Which of the following statements is/are correct ?

(1)It falls with a constant speed of

9.8

m s

^{-1}

.

(2)It falls

9.8

m every second.

(3)It has a speed of

19.6

m s

^{-1}

after

2

s.

42.

A particle is thrown vertically upwards. When the particle is at the maximum height, its acceleration is

43.

Stroboscopic photograph of a ball rolling down a slope with positions K, L, M, N, O, P at 0, 4, 16, 36, 64 and 100 cm

The above figure shows the stroboscopic photograph of a ball rolling down a slope. If the stroboscope makes $2$ flashes per second, in which region does the ball have an average speed of $40$ cm s $^{-1}$ ?

44.

Graph of displacement against (time)^2: straight line from the origin to 4 m at 4 s^2

An object is accelerated from rest along a straight line. The above graph shows the variation of its displacement with the square of time. What is the acceleration of the object ?

45.

Ticker-tape with dots separated by 1 cm, 2 cm, 3 cm, 4 cm, 5 cm and 6 cm

The diagram above shows a ticker-tape produced by a trolley being pulled by a rubber band. Which of the following statements about the trolley is/are true ?

(1)Its displacement increases uniformly with time.

(2)Its velocity increases with time.

(3)Its acceleration increases uniformly with time.

46.

A body falls freely from rest. What are the distances travelled in the first and third second ?

	First second	Third second
	$4.9$ m	$14.7$ m
	$4.9$ m	$19.6$ m
	$4.9$ m	$24.5$ m
	$9.8$ m	$39.2$ m

47.

Velocity-time graph: straight line from the origin to 6 m/s at t = 3 s

The graph shows the variation of the velocity of a car with time. What is the acceleration of the car ?

48.

A car moving with speed $50$ km h $^{-1}$ can be stopped in a distance of $15$ m. In what distance can the car be stopped when its speed is $70$ km h $^{-1}$ under the same condition ?

49.

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

50.

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