64. A lift descends with an acceleration of 0.5 m/sec2 from the top floor of a multistoreyed building. The time required to travel a distance of 25 m, will be

A. 5 sec

B. 8 seC

C. 10 sec

D. 12 sec

65. A stone is projected upwards from the foot of a towar 50 m high with a velocity of 25 m/sec and at the same time an other stone is dropped from the top of the tower. The two stones cross each other after

A. 2 sec

B. 3 sec

C. 4 sec

D. 5 sec

66. A particle starts from rest moves in a straight line whose equation of motion is given by s = t2 - 2t2 - 1. The acceleration of the particle after one sec, will be

A. 1 m/sec2

B. 2 rn/sec2

C. 3 m/sec2

D. 4 m/sec2.

67. The motion of a moving car is given by the equation a = t3 + 3t2 + 5 where a is the acceleration in m/sec2 and t is the time in seconds. The velocity of the car after 2 secs, will be

A. 4 m/sec

B. 8 m/sec

C. 12 m/sec

D. 22 m/sec.

68. Ifs is the distance traversed by a particle within a time t, its acceleration is

A.(b) d2 sdt2

B.(d) none of these.

C.

D.

69. If rain falls in the opposite direction of the movement of a pedestrian, he has to hold his umbrella

A. more inclined when moving

B. less inclined when moving

C. more inclined when standing

D. less inclined when standing.

70. To a cyclist riding west at 20 kg per hour, the rain appears to meet him at an angle of 45? with the vertical. When he rides at 12 km per hour, the rain meets him at an angle of 19? 48' with the vertical, the actual direction of the rain, is

A. 13?

B.b) 21?

C. 31?

D. 70?.

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