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.

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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%.

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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

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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

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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%.

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216. For a self-locking machine, the efficiency should be
A. less than 60%
B.50%
C. more than 50%
D. None of these.

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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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