A ball is thrown straight up in the air with a speed of 30 m/s. How much time does it take for the ball to return to the thrower? The acceleration due to gravity has an exact value of 9.8 m/s2, but you may use 10 m/s2. Hint: what would the final velocity be? Make sure to include the positive or negative in that final velocity
U=30m/s²
V= 0
V = u -gt
0 = 30 - 10t
t=3s
That was the time up, but they want total time in the air.
We have not learned that second part yet. All we were told was to use the equation Vf=Vo+at and I plugged in
-30=30+10(t) but all I get is -6 not 6
but a is down, negative
-30 = 30 - 10 t
10 t = 60
t = 6 seconds
(that is the quickest way to do it. I was trying to lead you through everything that is going on.)
Yes
Or would Vf^2+Vo^^2+2a(Xf-Xo) work
Is really what I used to get the height
v^2 = 2 g h
Thank you!!
You are welcome.
V = Vo + g*Tr = 0.
30 - 9.8Tr = 0,
Tr = 3.06 s. = Rise time.
Tf = Tr = 3.06 s.
Tr+Tf = 3.06 + 3.06 = 6.12 s. = Time in air.
final velocity will be 30 down or -30m/s
to get time up:
(1/2) m v^2 at bottom = m g h at top
so
30^2 = 2 g h
h = 900/(2*10) = 90/2 = 45 meters
average speed up = 30/2 = 15 m/s
so time up = 45/15 = 3 seconds
time down is also 3
so
6 seconds in the air