Answer:
a) The rocket reaches a maximum height of 737.577 meters.
b) The rocket will come crashing down approximately 17.655 seconds after engine failure.
Explanation:
a) Let suppose that rocket accelerates uniformly in the two stages. First, rocket is accelerates due to engine and second, it is decelerated by gravity.
1st Stage - Engine
Given that initial velocity, acceleration and travelled distance are known, we determine final velocity (
), measured in meters per second, by using this kinematic equation:
(1)
Where:
- Acceleration, measured in meters per square second.
- Travelled distance, measured in meters.
- Initial velocity, measured in meters per second.
If we know that
,
and
, the final velocity of the rocket is:
![v = \sqrt{\left(0\,\frac{m}{s} \right)^{2}+2\cdot \left(2.35\,\frac{m}{s^{2}} \right)\cdot (595\,m)}](https://tex.z-dn.net/?f=v%20%3D%20%5Csqrt%7B%5Cleft%280%5C%2C%5Cfrac%7Bm%7D%7Bs%7D%20%5Cright%29%5E%7B2%7D%2B2%5Ccdot%20%5Cleft%282.35%5C%2C%5Cfrac%7Bm%7D%7Bs%5E%7B2%7D%7D%20%5Cright%29%5Ccdot%20%28595%5C%2Cm%29%7D)
![v\approx 52.882\,\frac{m}{s}](https://tex.z-dn.net/?f=v%5Capprox%2052.882%5C%2C%5Cfrac%7Bm%7D%7Bs%7D)
The time associated with this launch (
), measured in seconds, is:
![t = \frac{v-v_{o}}{a}](https://tex.z-dn.net/?f=t%20%3D%20%5Cfrac%7Bv-v_%7Bo%7D%7D%7Ba%7D)
![t = \frac{52.882\,\frac{m}{s}-0\,\frac{m}{s}}{2.35\,\frac{m}{s} }](https://tex.z-dn.net/?f=t%20%3D%20%5Cfrac%7B52.882%5C%2C%5Cfrac%7Bm%7D%7Bs%7D-0%5C%2C%5Cfrac%7Bm%7D%7Bs%7D%7D%7B2.35%5C%2C%5Cfrac%7Bm%7D%7Bs%7D%20%7D)
![t = 22.503\,s](https://tex.z-dn.net/?f=t%20%3D%2022.503%5C%2Cs)
2nd Stage - Gravity
The rocket reaches its maximum height when final velocity is zero:
(2)
Where:
- Initial speed, measured in meters per second.
- Final speed, measured in meters per second.
- Gravitational acceleration, measured in meters per square second.
- Initial height, measured in meters.
- Final height, measured in meters.
If we know that
,
,
and
, then the maximum height reached by the rocket is:
![v^{2} -v_{o}^{2} = 2\cdot a\cdot (s-s_{o})](https://tex.z-dn.net/?f=v%5E%7B2%7D%20-v_%7Bo%7D%5E%7B2%7D%20%3D%202%5Ccdot%20a%5Ccdot%20%28s-s_%7Bo%7D%29)
![s-s_{o} = \frac{v^{2}-v_{o}^{2}}{2\cdot a}](https://tex.z-dn.net/?f=s-s_%7Bo%7D%20%3D%20%5Cfrac%7Bv%5E%7B2%7D-v_%7Bo%7D%5E%7B2%7D%7D%7B2%5Ccdot%20a%7D)
![s = s_{o} + \frac{v^{2}-v_{o}^{2}}{2\cdot a}](https://tex.z-dn.net/?f=s%20%3D%20s_%7Bo%7D%20%2B%20%5Cfrac%7Bv%5E%7B2%7D-v_%7Bo%7D%5E%7B2%7D%7D%7B2%5Ccdot%20a%7D)
![s = 595\,m + \frac{\left(0\,\frac{m}{s} \right)^{2}-\left(52.882\,\frac{m}{s} \right)^{2}}{2\cdot \left(-9.807\,\frac{m}{s^{2}} \right)}](https://tex.z-dn.net/?f=s%20%3D%20595%5C%2Cm%20%2B%20%5Cfrac%7B%5Cleft%280%5C%2C%5Cfrac%7Bm%7D%7Bs%7D%20%5Cright%29%5E%7B2%7D-%5Cleft%2852.882%5C%2C%5Cfrac%7Bm%7D%7Bs%7D%20%5Cright%29%5E%7B2%7D%7D%7B2%5Ccdot%20%5Cleft%28-9.807%5C%2C%5Cfrac%7Bm%7D%7Bs%5E%7B2%7D%7D%20%5Cright%29%7D)
![s = 737.577\,m](https://tex.z-dn.net/?f=s%20%3D%20737.577%5C%2Cm)
The rocket reaches a maximum height of 737.577 meters.
b) The time needed for the rocket to crash down to the launch pad is determined by the following kinematic equation:
(2)
Where:
- Initial height, measured in meters.
- Final height, measured in meters.
- Initial speed, measured in meters per second.
- Gravitational acceleration, measured in meters per square second.
- Time, measured in seconds.
If we know that
,
,
and
, then the time needed by the rocket is:
![0\,m = 595\,m + \left(52.882\,\frac{m}{s} \right)\cdot t + \frac{1}{2}\cdot \left(-9.807\,\frac{m}{s^{2}} \right)\cdot t^{2}](https://tex.z-dn.net/?f=0%5C%2Cm%20%3D%20595%5C%2Cm%20%2B%20%5Cleft%2852.882%5C%2C%5Cfrac%7Bm%7D%7Bs%7D%20%5Cright%29%5Ccdot%20t%20%2B%20%5Cfrac%7B1%7D%7B2%7D%5Ccdot%20%5Cleft%28-9.807%5C%2C%5Cfrac%7Bm%7D%7Bs%5E%7B2%7D%7D%20%5Cright%29%5Ccdot%20t%5E%7B2%7D)
![-4.904\cdot t^{2}+52.882\cdot t +595 = 0](https://tex.z-dn.net/?f=-4.904%5Ccdot%20t%5E%7B2%7D%2B52.882%5Ccdot%20t%20%2B595%20%3D%200)
Then, we solve this polynomial by Quadratic Formula:
, ![t_{2} \approx -6.872\,s](https://tex.z-dn.net/?f=t_%7B2%7D%20%5Capprox%20-6.872%5C%2Cs)
Only the first root is solution that is physically reasonable. Hence, the rocket will come crashing down approximately 17.655 seconds after engine failure.