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NEET PHYSICSEasy

The mass of a lift is 2000 kg2000 \text{ kg}. When the tension in the supporting cable is 28000 N28000 \text{ N}, its acceleration is:

A

30 ms−230 \text{ ms}^{-2} downwards

B

4 ms−24 \text{ ms}^{-2} upwards

C

4 ms−24 \text{ ms}^{-2} downwards

D

14 ms−214 \text{ ms}^{-2} upwards

Step-by-Step Solution

  1. Identify Forces: The forces acting on the lift are the tension (TT) in the cable acting upwards and the weight (mgmg) of the lift acting downwards.
  2. Compare Forces:
  • Tension, T=28000 NT = 28000 \text{ N}.
  • Weight, W=mg=2000 kg×10 ms−2=20000 NW = mg = 2000 \text{ kg} \times 10 \text{ ms}^{-2} = 20000 \text{ N} (assuming g≈10 ms−2g \approx 10 \text{ ms}^{-2}).
  • Since T>mgT > mg (28000>2000028000 > 20000), the net force is acting upwards, meaning the lift accelerates upwards.
  1. Apply Newton's Second Law: The net force FnetF_{net} equals mass times acceleration (mama). Fnet=T−mg=maF_{net} = T - mg = ma 28000−20000=2000×a28000 - 20000 = 2000 \times a 8000=2000a8000 = 2000 a
  2. Calculate Acceleration: a=80002000=4 ms−2a = \frac{8000}{2000} = 4 \text{ ms}^{-2} Direction is upwards. (Reference: NCERT Class 11, Physics Part I, Chapter 5, Laws of Motion, Section 5.9 Common Forces in Mechanics).
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