Problema Solution
If an m-16 is fired straight upward, then the height (h)t of the bullet in feet at time t in seconds is given by h(t)= -16t2+325t
a) What is the height of the bullet 5 seconds after it is fired? Evaluate h(5) and conclude.
b) How long does it take for the bullet to return to earth?
Answer provided by our tutors
a) t = 5 seconds we plug into h(t)= -16t2+325t
h(5) = - 16*5^2 + 325*5
h(5) = 1225 ft
after 5 seconds the bullet will be 1225 ft above the ground.
b) the bullet will return to earth when h(t) = 0
0 = - 16t^2 + 325t
- 16t^2 + 325t = 0
t(-16t + 325) = 0
h(t) = 0 at the start moment when t = 0 s
h(t) = 0 when the bullet returns to earth when -16t + 325=0 that is t = 20.3125 s
it takes 20.3125 s for the bullet to return to earth.