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Need help with maths homework question

question:

A lorry starts from rest at a set of traffic lights and accelerates uniformly to 90km h^-1 in 15 seconds.

a) what is the acceleration of the lorry?


b) how far has the lorry traveled in this time?

I believe I used SUVAT equations. I have done some calculations but I'm not sure if they are 100% correct.
Reply 1
sorry not sure what h^-1 means, but for a) just looking at it should be -6km/second
Reply 2
Original post by hollyschool
sorry not sure what h^-1 means, but for a) just looking at it should be -6km/second


90kmh^-1 is same as just 90km/h
Reply 3
ahh okay :smile:
(edited 5 years ago)
Reply 4
You only need SUVAT for these questions.
Original post by ikninja1
question:

A lorry starts from rest at a set of traffic lights and accelerates uniformly to 90km h^-1 in 15 seconds.

a) what is the acceleration of the lorry?


b) how far has the lorry traveled in this time?

I believe I used SUVAT equations. I have done some calculations but I'm not sure if they are 100% correct.


for a) you can simply use a= (v-u)/t where u=0 and v= 90km/hr and t=15 seconds. I would convert the final speed to m/s to stick with SI units but technically you can still keep it in km/hr.

b) there's a bunch of different ways you can do this but easiest is s=0.5(u+v)t
Original post by hollyschool
ahh okay :smile: well the answer is 6km/second


I'm afraid that is incorrect
Reply 7
Original post by Anonymouspsych
for a) you can simply use a= (v-u)/t where u=0 and v= 90km/hr and t=15 seconds. I would convert the final speed to m/s to stick with SI units but technically you can still keep it in km/hr.

b) there's a bunch of different ways you can do this but easiest is s=0.5(u+v)t



Ah cool, thanks, I believe I worked it out.

a)1.67m/s^2
b)187.5m
Original post by ikninja1
Ah cool, thanks, I believe I worked it out.

a)1.67m/s^2
b)187.5m


yep you're right :smile:

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