Friday
September 19, 2014

Homework Help: Physics

Posted by JC on Thursday, November 6, 2008 at 6:26am.

Sorry for posting so many, but I just need to make sure I'm on the right track.

Just need someone to check my working and answers.

A rocket has a mass 3000kg. The fuel used in the rocket has an additonal mass of 500kg. At the launch, the rocket accelerates at 4m/s/s. Using 10m/s/s as gravity.

a) Calculate the net force on the rocket.

f=ma (Newton's 2nd Law)
=3500 x 4
=14000 N

b) What is the weight of the rocket at launch?

w=mg
=3500 x 10
=35000N

c) Determine the upward force exerted by the rocket motors at the instant of the launch

F(net)=W + F(up)
=35000 + (4 x 35000)
=175000N (upwards)

d) The rocket takes 3 minutes to burn all of it's fuel. If the rocket motors suply a constant force, would you expect the acceleration to remain constant during the first 3 minutes. Explain your answer.

No. If the rocket takes 3 mintues to burn all of it's fuel, during that time, the mass of the fuel decreases. Since the force remains the same thorughout the 3 mintues, the rocket will accelerate when there is less mass.

Determine
e) the upward force acting on the rocket after the fuel tank beocme empty.

F(up)=0N

f)the acceleration of the rocket after this instant.

10m/s/s due to gravity.

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