MOTION UNDER GRAVITY

36. A stone released with zero velocity from the top of tower reaches the ground in 4 sec. If $g = 10 m / s e c^{2}$ , then the height of the tower is

20 m

40 m

80 m

160 m

37. A ball thrown vertically upward returns to its starting point in 4 s. Its initial speed is

23.6 m/s

m / s

19.6 m/s

zero

38. A stone is thrown down-vertically from the top of a tower with an initial velocity of $10 m s^{- 1}$ . It strikes the ground after 2 sec. The velocity with which the stone strikes the ground is ${g=10~m/s^{2})$

20 m / s

30 m s^{- 1}

40 m / s

10 m / s

39. A ball is released from the top of a tower of height h metres. It takes T seconds to reach the ground. Where is the ball at the time $T / 2$ seconds?

h / 2

metres from the ground

h / 4

metres from the ground

3 h / 4

metres from the ground

depends upon the mass and volume of the ball

42. A stone thrown vertically upward flies past a window one second after it was thrown upward and after three seconds on its way downward, the initial velocity of the stone is

10 ms-1

20 ms-1

15 m / s

5 m/s

43. What is maximum height of a stone thrown vertically upward if its velocity is halved in 1.5 second? $(g = 10 m s^{- 2})$

20 m

25 m

30m

45m.

44. A stone thrown upward with a speed u from the top of the tower reaches the ground with a velocity 3u. The height of the tower is

3 u^{2} / g

4 u^{2} / g

6 u^{2} / g

u^{2} / g

45. A balloon is at a height of 81 meters and is ascending upwards with a velocity of $12 m / s$ . A body of 2 kg weight is dropped from it. If $g = 10 m / s^{2}$ , the body will reach the surface of the earth in

1.5 s

4.025 s

5.4s

6.75 s

46. A body falls freely from the top of a tower and it falls $7 / 16$ th of the total distance in its last second. The time taken by the body to complete motion is

3 seconds

4 seconds

5 seconds

6 seconds

47. A body of mass 2 kg is released at the top of a smooth inclined plane having inclination $30^{\circ}$ It takes 3 seconds to reach the bottom. If the angle of inclination is doubled (made $60^{\circ}$ ), what will be the time taken?

3 second

{(3)}^{1 / 2}

second

1 / {(3)}^{1 / 2}

second

None of these.

50. Two balls of the same masses are thrown upwards at an interval of 2 seconds, along the same vertical line with the same initial velocity of $39.2 m s^{- 1}$ . They will collide at a height

44.1m

58.8 m

73.5 m

78.4 m

51. A balloon is going upwards with a velocity of 20 ms-1. It releases a packet when it is at a height of 160 m from the ground. The time taken by the packet to reach the ground will be $(g = 10 m s^{- 2})$ .

6 s

8 s

10 s

12 s

52. A ball is projected vertical upwards from the surface of earth with an initial speed $+ 49 m / s$ . The ball reaches its maximum height in 5.0 seconds. Neglecting air resistances, what is the total displacement of the ball from the time it is thrown until it returns to the point from which it was thrown.

248 m

9.8 m

49 m

0 m.

53. A stone falls freely from rest and the total distance covered by it in the last second of 9 its motion equals $9 / 25$ of its motion, the stone remains in air for

4 S

5 S

6 S

7 S

54. One body is dropped while a second body is thrown downward with an initial velocity of $l m / s e c$ simultaneously. The separation between these is 18 metres after a time

18 seconds

9 seconds

4.5 seconds

36 seconds

55. A particle is projected vertically upwards with a velocity u. Then

when it returns to the point of projection its displacement is

u^{2} / g

when it returns to the point of projection total distance covered by it is zero.

when it is at the maximum height its acceleration is zero.

when it returns to the point its average velocity is zero.