# motion problem (Help)

• Mar 8th 2009, 07:29 PM
VkL
motion problem (Help)
A rocket was launched upwards from the ground, and after 2 seconds, it was at a height of 96 feet.

a.) The initial velocity of the rocket was ______
b.) After 2 seconds the rocket was ____ (ascending / descending)
c.) The rocket reached a maximum height of _____
d.) The rocket landed when t =

- I dont' know how to start this problem. They did not give enouph information it seems.
• Mar 8th 2009, 07:38 PM
TheEmptySet
Quote:

Originally Posted by VkL
A rocket was launched upwards from the ground, and after 2 seconds, it was at a height of 96 feet.

a.) The initial velocity of the rocket was ______
b.) After 2 seconds the rocket was ____ (ascending / descending)
c.) The rocket reached a maximum height of _____
d.) The rocket landed when t =

- I dont' know how to start this problem. They did not give enouph information it seems.

$\displaystyle y(t)=\frac{1}{2}a+v_0t+y_0$

but we know (I think ) $\displaystyle g=-32\frac{ft}{s^2}$ and that$\displaystyle y_0=0$

$\displaystyle y(t)=-16\frac{ft}{s}t^2+v_0t$

we also know that $\displaystyle y(2)=96$ so we get

$\displaystyle 96ft=-64ft+2v_0 \iff v_0=80\frac{ft}{s}$

so know we know the equation is

$\displaystyle y(t)=-16t^2+80t=-16t(t-5)$

You should be able to finish from here.

Good luck.