Question

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

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