NCERT Solutions for Class 11 Science Newton’s law of motion and friction 3
Important Board Questions
Newton’s law of motion and friction
NCERT Books for Session 2022-2023
CBSE Board and UP Board
Two Marks Questions
A spring balance is attached to the ceiling of a lift. When the lift is at rest spring balance reads 49 N of a body hang on it. If the lift moves : (i) Downward (ii) upward, with an acceleration of 5 ms⁻² (iii) with a constant velocity. What will be the reading of the balance in each case?
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(i) R = m (g – a)
weight = 49 N
so m = 49/9.8 = 5kg
R = 5 (9·8 – 5)
R = 24N
(ii) R = m (g + a)
R = 5 (9·8 + 5)
R = 74 N
(iii) as a = 0 so R = mg = 49N