question_answer

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/s2)

A) 9 s and 1800 m                  

B) 8 s and 1500 m

C) 3 s and 2000 m  

D) 5 s and 500 m

Correct Answer: A

Solution :

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                                    \[h=ut+\frac{1}{2}g{{t}^{2}}\] 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    \[=200\times 9\] = 1800 m