When the rocket reaches its maximum height, what is its kinetic energy?

[laurenyntema]

1. A model rocket with a mass of 4.3kg is launched straight up at a speed of 65m/s. Kinetic energy when it takes off is 9083.75 J. Total energy when it takes off is also 9083.75J. When the rocket reaches its maximum height, what is its kinetic energy?



2. KE(kinetic energy)=1/2MV^2



3. KE= 1/2(4.3)(65^2)
KE=1/2(4.3)(4225)
KE=1/2(18167.5)
KE=9083.75... not sure where to go from here...

 

[mikelepore]

Consider what its speed will be, just as it reaches the maximum height, and an instant before it begins to fall back down.

 

[inventorjack]

To add to what mikelepore noted, remember that generally kinetic energy has to do with movement, and that with things like rockets and pendulums and such, the kinetic energy decreases as the potential energy increases. You're launching straight up, so you only have to worry about what's happening on a single axis.

 

[laurenyntema]

Ok, thanks!
I actually understand! Because kinetic energy is the energy due to motion, at maximum height the rocket would have a velocity of 0. Therefore, since there is actually no action taking place the kinetic energy is 0.

 

[inventorjack]

Exactly :)

And conversely, it's potential energy is now at maximum.