SOLUTION: An object is propelled vertically upward with an initial velocity of 20 meters per second. The distance s(in meters) of the object from the ground after t seconds is s = -4.9t^2 +

Question 1207437: An object is propelled vertically upward with an initial velocity of 20 meters per second. The distance s(in meters) of the object from the ground after t seconds is s = -4.9t^2 + 20t.

(a) When will the object be 15 meters above the ground?

I think here I must let s = 15 and solve for t. Yes?

(b)When will it strike the ground?

I think here s = 0 and solving for t is needed. Yes?

(c)Will the object reach a height of 100 meters?

I think here s = 100 and I must solve for t.

Yes?
Answer by ikleyn(52776) (Show Source): You can put this solution on YOUR website!
.


(a)  Yes.


(b)  Yes.


(c)  Yes.  Try to solve this equation.

           If there is a real positive solution for time, then your answer to (c) is positive.

           If there is no real positive solution for time, then your answer to (c) is negative.

I answered all your questions.

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In this site, there is a bunch of lessons on a projectile thrown/shot/launched vertically up

    - Introductory lesson on a projectile thrown-shot-launched vertically up
    - Problem on a projectile moving vertically up and down
    - Problem on an arrow shot vertically upward
    - Problem on a ball thrown vertically up from the top of a tower
    - Problem on a toy rocket launched vertically up from a tall platform
    - A flare is launched from a life raft vertically up

Consider these lessons as your textbook, handbook, tutorials and (free of charge) home teacher.
Read them attentively and learn on how to solve this type of problems once and for all.

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