# Calculus Gravity Question?

Hi, i have a practice problem i need help with.

### 3 Answers

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- AlanLv 71 month ago
your first equation is position .

d(t) = 4.9t^2

but you want velocity = 98 m/s

v(t) = 9.8t

9.8t = 98

t = 98/9.8 = 10 seconds

now , plug 10 seconds back into your distance equation

d(10 seconds) = 4.9(10)^2 = 4.9*100 = 490 meters

so you need to be 490 meters high to reach

a speed of 98 m/s when you hit the ground

- nbsaleLv 61 month ago
The speed will be the derivative of the distance, so at time t the speed is

v(t) = d'(t) = 9.8t.

That fits with the physics, because the acceleration due to gravity is 9.8m/s^2.

Now find t such that v(t) = 98, and plug that value into d(t).

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"I rearranged it so 98=4.9t^2," No, that's not what I said to do. Read it carefully.