# Acceleration and speed? Physics/maths? Pls help...?

How would you go calculate this:

1) A rocket has an average speed of 5000 km per hour.

Travelling at this speed, how long would it take the rocket to travel

12,740km?

2 From take off, the rocket can get upto 2 km/s in 14 seconds. What's the acceleration of the rocket in m/ss?

^

I know the units for acceleration

are metres per second squared,

but my computer doesn't do the

little '2' for squared.

I'm NOT asking people to do my homework for me, i'm just asking

1) The sums i would need to do to calculate these things

and

2) Why?

Thanks very much =]

Relevance

1) distance = rate * time. the time result will be in hours.

2) a = dv/dt. the result will be in km/s^2. divide that by 1000 to get the acceleration in m/s^2, because 1km=1000m.

http://en.wikipedia.org/wiki/Uniform_acceleration

especially the Formulae section

cheers

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• 1. Speed of rocket = 5000km/h meaning that, in one hour, the rocket covers 5000km.

you just need to use proportions.

5000km is covered in 1h

12 740 km will be covered in (1/5000)(12 740) = 2.548h

2.. acceleration = rate of change of velocity, i.e change in velocity divide by the time taken.

when the rocket takes off, its velocity changes from 0km/s to 2km/s. this occurs within 14s.

so, acceleration = (2 - 0)/14 = 0.14 kilometer per second square.

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• 1) if the distance and speed are calculated from earth reference frame, the way is to simply use distance=speed *time. But if youi change the reference frame this wont be valid.

2)the rocket may have variable accn but to an avg it is simply 142.8 m/s^2

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