Question

If we send a rocket at the surface of the earth to reach a height of 4.0 x 10^5 m ABOVE Earth's surface. Which of the following would be zero?

Please check this answer.


total energy (before)= total energy (after)

Epi + Eki = Epf + Ekf

My teacher assumes Ekf is zero, but my questions is why Eki is not zero? because when we start, how do we know if the object was not stationary and Vi= 0 m/s ???

Answer 1

Vi not = 0

Answer 2

If Vi=0
Then it can not go to up

Answer 3

U r just throwing rocket with a big velocity to the sky

Answer 4

Velocity of rocket is decreasing when it is going upward

Answer 5

Let the velicity of rocket on earth =100m/s

Answer 6

Velocity of rocket above 10km on earth=90km/s

Answer 7

Just guess

Answer 8

At last the final velocity of rocket=0

Answer 9

U know
P.E on earth=mgh=mg*0=0

Answer 10

I can make it clearer by chating here

Answer 11

A rocket is not a cannonball. It is powered by fuel engines.
Mechanical energy is not conserved in the case of a rocket.
So this problem sucks.
It should read : "If we send a cannonball..."

Answer 12

Thank you @shamim and @Vincent-Lyon.Fr

@Vincent-Lyon.Fr yes, in physics 12, students sometime have to deal with unrealistic situations, but you are completely right. Energy cannot be conserved in this situation.