Solved: PHYSICS Question for NEET

NEET PHYSICSMedium

If a person with a spring balance and a body hanging from it goes up and up in an aeroplane, then the reading of the weight of the body as indicated by the spring balance will:

Go on increasing

Go on decreasing

First increase and then decrease

Remain the same

Step-by-Step Solution

Initial Ascent (Acceleration Phase): When the aeroplane takes off and ascends, it accelerates vertically upwards with acceleration $a$ . According to Newton's Second Law, the force (tension $T$ in the spring balance) is given by $T - mg = ma$ , so $T = m(g + a)$ . This apparent weight is greater than the actual weight ( $mg$ ). Thus, the reading increases initially.
High Altitude Phase (Variation of g): As the aeroplane reaches higher altitudes ('goes up and up'), the acceleration due to gravity ( $g$ ) decreases with height ( $h$ ) according to the relation $g_h = g \frac{R^2}{(R+h)^2}$ . As $g$ decreases, the weight ( $mg'$ ) decreases.
Cruising Phase: Additionally, when the plane reaches a steady cruising altitude, the vertical acceleration $a$ becomes zero, returning the apparent weight to $mg'$ (which is already lower than ground $mg$ due to altitude).
Conclusion: Consequently, the reading first increases due to the initial upward acceleration and subsequently decreases due to the decrease in gravity at high altitudes. (Reference: NCERT Class 11, Physics Part I, Chapter 5: Laws of Motion [Apparent Weight]; Chapter 8: Gravitation [Variation of g]).

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