A projectile is shot from the ground at a velocity of #7 m/s# and at an angle of #(7pi)/12#. How long will it take for the projectile to land?

1 Answer
Oct 3, 2016

Let the velocity of projection of the projectile be u with angle of projection #alpha# with the horizontal direction.
The vertical component of the velocity of projection is #usinalpha# and the horizontal component is #ucosalpha#

Now if the time of flight be T then the object will return to the ground after T sec and during this T sec its total vertical displacement h will be zero. So applying the equation of motion under gravity we can write
#h=usinalphaxxT+1/2gT^2#

#=>0=uxxT-1/2xxgxxT^2#

#"where "g = "acceleration due to gravity"#

#:.T=(2usinalpha)/g#

In the given problem

#u=7"m/s" and alpha=(7pi)/12 " "g=9.8m/s^2#

#T=(2xx7xxsin((7pi)/12))/9.8=1.38s#