SOLUTION: A projectile is fired from the ground with an upward speed of 245m/s. After how many seconds will it return to the ground? use the formula {{{h=vt-4.9t^2}}}

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Question 206638: A projectile is fired from the ground with an upward speed of 245m/s. After how many seconds will it return to the ground? use the formula h=vt-4.9t%5E2
Answer by Targetweek(62) About Me  (Show Source):
You can put this solution on YOUR website!
well first use the equation...
- Vf+=+Vi+-+gt (where Vf = final velocity, Vi = initial velocity)
and solve for t
Since the velocity is zero at the peak that's our final velocity
- 0+=+245+-+%289.81%29%28t%29
- 0-245+=+245-245-9.81t
- -245+=+-9.81t
- -245%2F-9.81+=+%28-9.81t%29%2F-9.81
- -245%2F-9.81+=+%28cross%28-9.81%29t%29%2Fcross%28-9.81%29
- 24.97+=+t
- so the projectile took 24.97 seconds to reach the peak
To find how long before it hit the ground simply double the time it took to reach the peak so...
24.97%2A2+=+49.94
So the projectile took 49.94 seconds to return to the ground