Question

A 33 tonnes jet airline has 4 engines,each producing a nearly constant thrust of 165kN during the takeoff roll.Determine the length of the runway required if the takeoff speed is 320km/h.Neglect air and rolling resistance.

Answer 1

320,000 m/h /3600s/h = 88.9 m/s

v = a t
d = (1/2) a t^2
so
d= (1/2) v^2/a
d = (1/2) (88.9)^2/a

but a = 4*165,000 N /33,000 kg
= 20.6 m/s^2 (2 g, good grief)

so d = (1/2)(88.9)^2/20.6
= 191.6 meters

Answer 2

so there is no need to consider about the weight when finding the force? since F=ma, then i use 165000x4=33000xa to find acceleration rather than 165000x4-33000=33000xa ?

Answer 3

That is correct
and if you were to use the weight for example to calculate a friction force you would do weight = mg, not just m