<p>A rocket moves upward, starting from rest with an acceleration of +29.4 m/s2

Question

<p>A rocket moves upward, starting from rest with an acceleration of +29.4 m/s2 for 4.00 sec.&#160; It runs out of fuel at the end of this&#160; 4.00 sec and continues to move upward.&#160; How high does it rise?&#160;</p>
<p>I used v=vo + at2 to find that the rocket moves upward 470.4 meters in the first four seconds.&#160; The class TA told me I would need to find an additional equation (where I am stuck) using a=-9.8 m/s2 (which I understand why)and having an intial velocity of 117.6 m/s (which I understand why but not how).&#160; Adding these two should add to 941m total.&#160;</p>

Explanation / Answer

the first part where to a = 29.4
here the body travels taken into account of the gravity
thus we will consider it to be the only acceleration
s = ut +.5 at2

s= 235.2 m

v= at

v= 117.6 m/s

now the question is like free body question.

u=117.4 m/s

v= 0

a= -9.8 m/s2

so,

v2 = u2 +2as

s = 705.6 m

total s= 235.2 + 705.6 = 940.8 m

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