Question

An aircraft has a lift-off of $120km/h$. How long does it take the aircraft to become airborne if it has to be airborne after a takeoff run of $240m$?

• A. $15s$
  
• B. $14.4s$
  
• C. $16s$
  
• D. $13s$
  

Answer 1

The correct option is B $14.4s$

Speed of aircraft $v=120km/h=120\times 5/18m/s=100/3m/s$
Applying Ist eqn of motion
$v=u+at$
$100/3=0+a\times t$
$100/3t=a$
Applying 3rd eqn of motion,
$v^2=u^2+2aS$
${100/3}^2=0^2+2\times \left(100/3t\right)\times 240$

On solving above equation, we get $t=14.4s$