Question

Two partials are thrown horizontally in opposite directions from the same point from a height h with velocities 4 ms^-1 and 3ms^-1. Find the separation between them when their velocities are perpendicular .

• A. 0.15 s
• B. 0.25 s
• C. 0.35 s
• D. None of these

Answer 1

Answer: (C)

0.35 s

Answer 2

${\overrightarrow{V}}_{1} = - 4\widehat{i} - gt\widehat{j}$ and ${\overrightarrow{V}}_{2} = 3\widehat{i} - gt\widehat{j}$ are the velocities at any instant. For velocities to be perpendicular ${\overrightarrow{V}}_{1}.{\overrightarrow{V}}_{2}$ = 0

that is ${\overrightarrow{V}}_{1}.{\overrightarrow{V}}_{2}$ = 0 or t = $\sqrt{12/g^{2}}$ = 0.35 s

separation = (u₁ + u₂)t = 7(0.35) = 2.45 m.