Question

A stone is thrown upward with a speed 'u' from the top of a tower reaches the ground with velocity ' \(3u\) '. The height of the tower is ( \(g\) = acceleration due to gravity)

• A. \(\frac{3u^2}{g}\)
• B. \(\frac{4u^2}{g}\)
• C. \(\frac{6u^2}{g}\)
• D. \(\frac{9u^2}{g}\)

Hint:

Key: Always take downward as positive for such problems

Answer 1

The Correct Option is B

Concept: Equation of motion: \[ v^2 = u^2 + 2gh \]

Step 1: Substitute values. \[ (3u)^2 = u^2 + 2gh \] \[ 9u^2 = u^2 + 2gh \]

Step 2: Solve. \[ 8u^2 = 2gh \Rightarrow h = \frac{4u^2}{g} \]

Step 3: Conclusion.
Height = $\frac{4u^2}{g}$ Final Answer: Option (B)