Question 972009
A space craft flying in a straight course with a velocity 75km/s fires it's [sic] rocket motors  for 6.0 seconds. At the end of this time it's [sic] speed  is 120 km/s in the same direction.  Find(i) the space  craft's  average accleration while the motors are firing,
Change in speed = 120 - 75 = 45 km/sec
Accel = 45/6 = 7.5 km/sec/sec
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(ii) the distance  travelled by the space  craft in the first 10 seconds after the rocket motors having been in action for only 6.0s
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If you mean after the 6 second firing:
d = r*t = 120*10
d = 1200 kms
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If you mean 10 starting at the 6 second firing:
The average speed for the 6 seconds = (75 + 120)/2 = 97.5 km/sec
d = 97.5*6 + 4*120
d = 1065 kms
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PS  it's = it is