# A model rocket with a mass of 2.7kg is launched straight up from the ground at a speed of 110m/s. What is the rocket's mechanical energy when it takes off?

Nov 15, 2015

I found $16 k J$
We can choose the firing position as "zero" for Gravitation Potential Energy (height $h$ zero);
${E}_{\text{mec}} = U + K = m g h + \frac{1}{2} m {v}^{2}$
but $U = 0$ and so:
${E}_{\text{mec}} = 0 + K = K = \frac{1}{2} m {v}^{2} = \frac{1}{2} \left(2.7\right) {\left(110\right)}^{2} = 16 , 335 J \approx 16 k J$