2 objects 1 up and 1 down thrown

[runner1738]

An object is thrown downward with an initial speed of 9 m/s from a height of 40 m above the ground. At the same instant, a second object is propelled vertically from ground level with a speed of 14 m.s. The acceleration of gravity is 9.8 m/s^2. At what height above the ground will the two objects pass each other? Abswer in units of m?

 

[christinono]

Use the following kinematics formula and equal the distances they travel. Then, solve for time.

$$d = V_it+ \frac{1}{2}at^2$$

Same idea as this one. Equal the distances.

 

[runner1738]

i guess i just can't do math in general casue i got 9t + 1/2(9.8)t^2=14t+1/2(-9.8)t^2
9.8t^2-5t=0 , that i got .5102040816 * what though?

 

[christinono]

Remember, the one being thrown down has a NEGATIVE velocity (negative direction).

 

[runner1738]

ok gotcha i think, thanks for all the help

 

[runner1738]

ok this time around i got 2.346938976 from -9t+1/2(9.8)t^2=14t+1/2(-9.8)t^2, but the answer is supposed to be in m? and i have time

 

[christinono]

ok this time around i got 2.346938976 from -9t+1/2(9.8)t^2=14t+1/2(-9.8)t^2, but the answer is supposed to be in m? and i have time

From the time, you can find the distance. Just use the formula:

$$d=V_it + \frac{1}{2}at^2$$