Question

A ball is thrown vertically upward with an initial velocity of 128 feet per second. The distance in feet of the ball from the ground after t seconds is s= 128t – 16t2 what intervals of time is the ball less than 240 above the ground (after it is tossed until it returns to the ground)?

1. {x 0 sec < x < 3.5 sec and 4.5 sec > x > 8 sec}

2. {x 0 sec < x < 3 sec and 5 sec > x > 8 sec}

3. {x 0 sec < x < 2.5 sec and 5.5 sec > x > 8 sec}

4. {x 3 sec < x < 5 sec}

Answer 1

Let's find the total time the flight:

s(T) = 0 ==> 128t – 16t² = 0 ==> T = 8.

So, the intervals of time is the ball less than 240 above the ground are

0 < x < 3 and 5 < x < 8 (answer number 2).