Question

An aeroplane moving horizontally with a speed of $720km/h$ drops a food packet, while flying at a height of $396.9m$. The time taken by a food packet to reach the ground and in horizontal range is : $(g=9.8m/s^2)$

• A. 9 s and 1800 m
• B. 8 s and 1500 m
• C. 3 s and 2000 m
• D. 5 s and 500 m

Answer 1

Answer: (A)

Firstly convert the unit of velcotiy in metre per second, because velocity is given in $km/h$ and height in metre.

Horizontal velocity $=720km/h$
$=720\times \frac{5}{18}$
$=200m/s$
Vertical height of plane $=396.9m$
$h=ut+\frac{1}{2}g{t}^2$
Since, $u=0$, so
$396.9=\frac{1}{2}\times 9.8\times t^2$
$\Rightarrow t^2=81$
$\Rightarrow t=9s$
Horizontal range $=$ horizontal velocity $\times$ time
$=200\times 9$
$=1800m$