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Laws Of Motion

Question
CBSEENPH11020722

The mass of a lift is 2000 kg. When the tension in the supporting cable is 28000 N, then its acceleration is 

  • 30 ms-2 downward

  • 4 ms-2  upwards

  •  4 ms-2  downwards

  • 14 ms-2  upwards

Solution

B.

4 ms-2  upwards

Apparent weight > actual weight, then the lift is accelerating upward.
Lift is accelerating upward at the rate of a 
Hence, equation of motion is written as
R - mg = ma
28000-20000 = 2000a
a = 8000/2000 = 4 ms-2 upwards.