Hi I need help answering this question. I worked it on my own and derived an ans
ID: 1450683 • Letter: H
Question
Hi I need help answering this question. I worked it on my own and derived an answer but it was incorrect. The questions reads, "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 12.3 N until the engine is used up. Robert launches the rocket on a windless day, so that it will travel straight up, and uses his laser-range finder to measure the height of the rocket, when the engine cuts off is 14.6m. He also measures the rocket's peak height which is 19.1m. If the rocket has a mass of 0.713kg, how much work is done by the drag foce on the rocket during its ascent?"
So I started off with W=12.3(14.6) = 179.6 J = KE
KE = 1/2mv^2 so 179.6 = 1/2(0.713)v^2
then I said Height = 14.6 + (179.6 / 19.62) = 23.8 and finally W = (0.713) (9.81) (19.1-23.8)
My final answer was about -32J like I said was wrong. Please any help would be much appreciated on what went wrong. Thanks!
Explanation / Answer
its wrong when u calculated height=14.6+(179.6/19.62)
it should be like
height will go extra 19.1-14.6=4.5m
F is the drag force
retardation=Force/mass=F/0.713
v2=u2+2as
0=22.442+2(-F/0.713)4.5
F=39.895N
Work done by drag force=-39.895*4.5=-179.52J