Question

From a point on the ground at a distance $a$ from the foot of a pole, a ball is thrown, at an angle ${45}^o$ which just clears the top of pole and strikes the ground at a distance of $b$, on the other side of it. Height of the pole is

• A. $\frac{a^2}{a^2+b^2}$
• B. $\frac{ab}{a+b}$
• C. $\frac{b^2}{a^2+b^2}$
• D. None of these

Answer 1

The correct option is B $\frac{ab}{a+b}$


From question range of projectile is
$R=a+b$
From the equation of trajectory,
$y=x\tan \theta (1-\frac{x}{R})$
$h=a\tan {45}^o(1-\frac{a}{a+b})$
$h=\frac{ab}{a+b}$