Question

A stone is thrown vertically up from the top end of a window of height 1.8 m with a velocity of 8 m/s\(^1\). The time taken by the stone to cross the window during its downward journey is:
(Acceleration due to gravity \( g = 10 \) ms\(^{-2}\))

• A. \( 0.8 \) s
• B. \( 1.6 \) s
• C. \( 1.0 \) s
• D. \( 0.2 \) s

Hint:

Use kinematic equations to solve free-fall problems. - Time is always positive in motion calculations.

Answer 1

The Correct Option is D

Step 1: Use kinematic equation
Using the equation of motion: \[ h = ut + \frac{1}{2} g t^2. \] Substituting \( h = 1.8 \), \( u = 8 \), and \( g = 10 \): \[ 1.8 = 8t + \frac{1}{2} (10) t^2. \] Step 2: Solve for \( t \)
Rearrange: \[ 1.8 = 8t + 5t^2. \] Solving for \( t \), we get \( t = 0.2 \) s. Thus, the correct answer is \( \boxed{0.2} \) s.