211. A 49 kg lady stands on a spring scale in an elevator. During the first 5 sec, starting from rest, the scale reads 69 kg. The velocity of the elevator will be

A. 10 m/sec

B. 15 m/sec

C. 20 m/sec

D. 25 m/sec.

212. For lifting a load of 50 kg through a distance of 2.5 cm, an effort of 12.5 kg is moved through a distance of 40 cm. The efficiency of the lifting machine, is

A.60%

B.65%

C.70%

D. 75%.

213. A load of 500 kg was lifted through a distance of 13 cm. by an effort of 25 kg which moved through a distance of 650 cm. The mechanical advantage of the lifting machine is

A.15

B.18

C.20

D.26

214. A load of 500 kg was lifted through a distance of 13 cm. by an effort of 25 kg which moved through a distance of 650 cm The velocity ratio of the lifting machine as, is

A.50

B.55

C.60

D.65

215. A load of 500 kg was lifted through a distance of 13 cm. by an effort of 25 kg which moved through a distance of 650 cm The efficiency of the lifting machine, is

A.50%

B.40%

C.55%

D. 30%.

216. For a self-locking machine, the efficiency should be

A. less than 60%

B.50%

C. more than 50%

D. None of these.

217. The velocity ratio of an inclined plane of inclination 0 with horizontal for lifting a load is

A. sin

B. cos 6

C. tan 0

D. cosec 0.

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