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Laws of Motion question

2021 · 26 Feb · Shift 1 · Q64
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  5. /2021 · 26 Feb · Shift 1 · Q64

Laws of Motion question

2021 · 26 Feb · Shift 1 · Q64

JEE MainPhysicsLaws of MotionNumerical+4 / −1
A person standing on a spring balance inside a stationary lift measures 60 kg. The weight of that person if the lift descends with uniform downward acceleration of 1.8 m/s2 will be ‾\underline{\hspace{2cm}}​ N. [g = 10 m/s2]
Numerical answer
View written solutionFree

Correct answer: 492

  1. Interpret the spring balance reading in the stationary lift

    When the lift is stationary, the spring balance reads the person's apparent mass as 60 kg60\,\text{kg}60kg.

    Hence the actual mass of the person is m=60 kgm = 60\,\text{kg}m=60kg

  2. Find the actual weight of the person

    Actual weight is W=mg=60×10=600 NW = mg = 60 \times 10 = 600\,\text{N}W=mg=60×10=600N

  3. Lift descending with downward acceleration

    If the lift accelerates downward with acceleration a=1.8 m/s2a = 1.8\,\text{m/s}^2a=1.8m/s2, then the apparent weight (normal reaction by the spring balance) becomes N=m(g−a)N = m(g-a)N=m(g−a)

    Substituting the values: N=60(10−1.8)N = 60(10-1.8)N=60(10−1.8) N=60(8.2)N = 60(8.2)N=60(8.2) N=492 NN = 492\,\text{N}N=492N

  4. Final answer

    Therefore, the weight measured in the descending lift is 492 N\boxed{492\,\text{N}}492N​

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