Another problem using resultant forces.
A rocket with a mass of 20
000 kg uses a take off engine with a thrust of 250 000 N.
(a) Calculate the initial
acceleration of the rocket
(b) what happens to the acceleration of the rocket as it rises
into the air?
(Take 9 = 9.8 ms-2)
(a) Resultant force producing
acceleration = Thrust - Weight = 250 000 - 196 000 = 54 000 N
Initial acceleration
= F/m = 54 000/20 000 = 2.7 ms-2.
Notice that it is the RESULTANT force that has been used to calculate the
acceleration of the rocket.
(b) As the rocket rises the mass with decrease as the fuel
is used up and if we assume a constant thrust then the acceleration will increase. There is
also a small reduction in air friction as the rocket climbs although this might be balanced by
increased drag as the speed increases. The change in the pull of gravity will only be
significant after climbing hundreds of kilometres.