Question

A rocket is fired at a velocity of $80m/s$ from the ground level at an angle of $50$ degrees above the horizontal. The rocket is fire toward an $10m$ high wall, which is located $20m$ away. By how much does the rocket clear the top of the wall? (in m)

• A. $15$
  
• B. $13.2$
  
• C. $13$
  
• D. $12$
  

Answer 1

The correct option is B $13.2$

Equation of trajectory of projectile

$\Rightarrow y=x\tan \theta -\frac{g{x}^2}{2u^2\cos \theta }$

Putting $x=20m,\theta ={50}^o,u=80m/s$

$\Rightarrow y=20\tan 50-\frac{9.8\times {20}^2}{2\times {80}^2\times \cos 50}=23.2$

Distance by which the the clear off the wall $=23.2-10=13.2$

Hence correct answer is option $B$