Robert has just bought a new model rocket, and is trying to measure its flight c
ID: 1347695 • Letter: R
Question
Robert has just bought a new model rocket, and is trying to measure its flight characteristics. The rocket engine package claims that it will maintain a constant thrust of 12.6 N until the engine is used up. Robert launches the rocket on a windless day, so that it travels straight up, and uses his laser range-finder to meaure that the height of the rocket when the engine cuts off is 12.4 m. He also measures the rocket's peak height, which is 16.9 m. If the rocket has a mass of 0.713 kg, how much work is done by the drag force on the rocket during its ascent?
Explanation / Answer
Workdone by engine, W_engine = 12.6*12.4
= 156.24 J
Workdone by gravity, W_gravity = -0.713*9.8*16.9
= -118.1 J
Let W_drag is the workdone by the drag force.
Net workdone in the total motion = change in kinetic energy
W_engine + W_gravity + W_drag = 0
W_drag = -( W_engine + W_gravity)
=-(156.24 - 118.1)
= -38.14 J
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