question_answer

A spring balance is attached to the ceiling of a lift. A man hangs his bag on the spring and the spring reads 49 N, when the lift is stationary. If the lift moves downward with an acceleration of \[5\,m/{{s}^{2}}\], the reading of the spring balance will be                                                 [AIEEE 2003]

A) 24 N

B) 74 N 

C) 15 N

D) 49 N  

Correct Answer: A

Solution :

[a] In stationary position, spring balance reading

= mg = 49

\[m=\frac{49}{9.8}=5\,kg\]

When lift moves downward

mg - T = ma

Reading of balance

T = mg - ma

= 5 (9.8 – 5)

\[=5\times 4.8\]

= 24.0 N