A rocket of mass 6.0 kg takes off from the ground and goes straight up. During t

Question

A rocket of mass 6.0 kg takes off from the ground and goes straight up. During the first 100 meters of its ascent, the engine exerts a 80 newton upward force on the rocket. a) how much work does the engine do on the rocket during those first 100 meters? b) Assuming kinetic and potential are the only kinds of energy the rocket gains, how much kinetic energy does the rocket have at the moment it's 100 meters above the ground? (Hint: You'll need to use a formula for gravitational potential energy but not a formula for kinetic energy. Think about the relationship between work and energy. To keep the math less messy, approximate g as 10 m/s^2.) c) At height 100 meters, the rocket has 1850 joules of kinetic energy, which is less than your part b answer. Is energy not conserved , or is something else going on? Where are the "missing" joules?

Explanation / Answer

a)W=Fx =80*100=8000J b)PE =mgh =6*100*10 =6000J KE =8000-6000=2000J C)As the rocket cuts through the air, air resistance saps away some of its kinetic energy. Specifically, the nose of the rocket starts heating up, as does the air it touches. That heat energy has to come from somewhere—in this case, the rocket’s kinetic energy. So, the “missing” kinetic energy didn’t just disappear; it changed into another form, “heat.”

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