Question

A military aircraft takes 20 s to lift off from the runway. If the velocity of aircraft just before take-off is 360 km/hr, what would have been the velocity of the aircraft at t = 1 s after the start? (Assume constant acceleration)

• A. 15 km/hr
• B. 21 km/hr
• C. 24 km/hr
• D. 18 km/hr

Answer 1

Answer: (D)

Given Data:

Time taken by military aircraft, $t=20sec$

Velocity of aircraft, $v=360{kmh}^{-1}=\frac{5}{18}\times 360=100{ms}^{-1}$

Initial velocity of aircraft,$u=0{ms}^{-1}$

Step 1: Finding velocity after 1sec:

From first equation of motion first we will find acceleration,

$v=u+at$

$200=0+a\left(20\right)⟹a=10{ms}^{-2}$

So, velocity after 1sec will be,

$v=u+at$

$v=0+\left(10\right)\left(1\right)=10m{s}^{-1}$

So, the velocity of the aircraft at t = 1 s after the start: 10m/s