物理位置與運動 DSE、CE 選擇題（第 4 頁）

31.

A man takes $30$ s to walk $80$ m towards the east. He then takes $10$ s to run $60$ m towards the south. Which of the following statements is/are correct ?

(1)The magnitude of the resultant displacement of the man is

140

m.

(2)The average speed of the man is

4.3

m s

^{-1}

.

(3)The magnitude of the average velocity of the man is

2.5

m s

^{-1}

.

32.

The paper tape shown is obtained from a trolley moving with uniform acceleration. The frequency of the ticker-tape timer is $50$ Hz. Find the acceleration of the trolley.

Ticker-tape with a first section of 1.5 cm and a later section of 3.6 cm, each spanning five intervals

33.

An object is thrown vertically upwards from a point $A$ . It travels to the highest point $B$ and then falls back to $A$ . Neglecting air resistance, which of the following statements is/are true ?

(1)The total displacement of the object is zero.

(2)The acceleration of the object is constant throughout the motion.

(3)The time for the upward motion is longer than the time for the downward motion.

34.

Acceleration-time graph: constant acceleration until t0, then zero

The above diagram shows the variation of the acceleration of an object which is initially at rest. Which of the following velocity-time graphs correctly describes the motion of the object ?

35.

Which of the following displacement-time graphs describes the motion of a particle moving in a straight line with uniform deceleration ?

Four displacement-time graphs A to D: A straight line falling to zero; B straight line through the origin; C curve rising with decreasing slope; D curve rising with increasing slope

36.

Equilateral triangle ABC of side 3 m with arrows along AB and BC

A man takes $2$ s to walk from point $A$ to point $B$ , and then takes $3$ s to walk from point $B$ to point $C$ , where $ABC$ is an equilateral triangle of side $3$ m. Find the magnitude of his average VELOCITY from $A$ to $C$ .

37.

A man at the edge of a cliff above the sea, and a velocity-time graph falling linearly from 60 m/s at t = 0 through zero at 6 s to -120 m/s at 18 s

The above figure shows a man near the edge of a cliff projecting a stone vertically upwards. The stone reaches the sea after $18$ s. The graph shows the velocity - time for the motion of the stone. Find the height of the cliff. (Take $g = 10$ m s $^{-2}$ .)

38.

Strobe photograph of a ball rolling down a slope with successive separations 4 cm, 8 cm and 12 cm

The above figure shows the strobe photograph of a ball rolling down a slope. The stroboscope is flashing at a frequency of $5$ Hz. Find the acceleration of the ball.

39.

The figure shows the velocity-time graph of an object. Which of the following statements about the object is/are true ?

(1)Its acceleration in the first

10

s is

2

m s

^{-2}

.

(2)The total distance travelled is

250

m.

(3)It returns to its starting point after

25

s.

Velocity-time graph: rises from 0 to 20 m/s at 10 s, constant until 20 s, then falls to zero at about 25 s

40.

The graph shows how the square of velocity of an object undergoing uniform acceleration varies with displacement. The object is initially at rest and travels along a straight line. The acceleration of the object is

Graph of v squared against s: straight line from the origin to 6 m^2/s^2 at s = 3 m