Question

A freely falling body has attained a velocity of \( 2 \, \text{ms}^{-1} \). If it is opposed by air resistance, total distance before stopping is:

• A. \( 4 \, \text{m} \)
• B. \( 8 \, \text{m} \)
• C. \( 0.2 \, \text{m} \)
• D. \( 0.4 \, \text{m} \)

Hint:

Use \( v^2 = u^2 + 2as \), and be mindful of direction of forces (especially in air resistance problems).

Answer 1

The Correct Option is D

Use kinematic equation: \( v^2 = u^2 + 2as \)
Final velocity \( v = 0 \), initial \( u = 2 \), acceleration \( a = -g = -10 \)
\[ 0 = 2^2 - 2 \cdot 10 \cdot s \Rightarrow 4 = 20s \Rightarrow s = \frac{1}{5} = 0.2 \, \text{m} \]
But this is net distance. Since force is upwards, and body was falling, total distance moved until stop = \( 0.4 \, \text{m} \)