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bezimeni [28]
3 years ago
8

the initial vertical velocity of a rocket shot straight up is 42 meters per second. How long does it take for the rocket to retu

rn to earth? round your answer to the nearest tenth of a second. show all your work.
Mathematics
1 answer:
Snowcat [4.5K]3 years ago
8 0
It takes 4.3 seconds for the rocket to return to earth.

The equation is:
0=-9.8t^2+v_0t+h_0
where -9.8m/sec² is the acceleration due to gravity, v₀ is the initial velocity, and h₀ is the initial height.  We will go from the assumption that the rocket is launched from the ground, so h₀=0, and we are told that the initial velocity, v₀, is 42.  This gives us:

0=-9.8t^2+42t

We will use the quadratic formula to solve this.  The quadratic formula is:
x=\frac{-b\pm \sqrt{b^2-4ac}}{2a}

Plugging in our information we have:
t=\frac{-42\pm \sqrt{42^2-4(-9.8)(0)}}{2(-9.8)}
\\
\\=\frac{-42\pm \sqrt{1764-0}}{-19.6}
\\
\\=\frac{-42\pm \sqrt{1764}}{-19.6}
\\
\\=\frac{-42\pm 42}{-19.6}=\frac{-42-42}{-19.6} \text{ or } \frac{-42+42}{-19.6}
\\
\\=\frac{-84}{-19.6}\text{ or }\frac{0}{-19.6}
\\
\\=4.3\text{ or }0

x=0 is when the rocket is launched; x=4.3 is when the rocket lands.
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