MHT CET · Maths · Application of Derivatives

A stone is dropped into a pond. Waves in the form of circles are generated and radius of outermostripple increases at the rate of $5 c m / s e c .$ Then area increased after $2$ seconds is ________

A $100 π {c m}^{2} / s e c$
B $40 {c m}^{2} / s e c$
C $50 {c m}^{2} / s e c$
D $25 {c m}^{2} / s e c$

Verified Solution

Answer & Solution

Correct Answer

(A) $100 π {c m}^{2} / s e c$

Step-by-step Solution

Detailed explanation

Given:

\frac{d r}{d t} = 5 c m / s e c \Rightarrow d r = 5 d t

t h e n r = 5 t + c,

t = 0, \Rightarrow r = 0 \Rightarrow c = 0

r = 5 t

New

A = π r^{2} \Rightarrow \frac{d A}{d t} = 2 π r \frac{d r}{d t}

= 2 π . 10.5

t = 2 \Rightarrow r = 10

= 100 π c m^{2} / s e c .

Apply the relevant identity from the chapter and substitute the values established in the previous step, keeping the original constraint in view.

Use the simplified expression to isolate the unknown, then plug the result back into the question setup to confirm the working is internally consistent.

Cross-check against a boundary or limiting case. Both the dimensional balance and the qualitative behaviour at the extreme should agree with the candidate answer.

Combine the steps above to identify the correct option. The remaining choices each fail at least one of the consistency, dimensional, or boundary checks.

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A stone is dropped into a pond. Waves in the form of circles are generated and radius of outermostripple increases at the rate of 5cm/sec. Then area increased after 2 seconds is ________

Step-by-step Solution

A stone is dropped into a pond. Waves in the form of circles are generated and radius of outermostripple increases at the rate of $5 c m / s e c .$ Then area increased after $2$ seconds is ________