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need help. physics question.

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highly_ambitious:
A cyclist is free-wheeling down a long straight hill. The times between passing successive kilometre posts are 100 seconds and 80 seconds. Assuming his acceleration is constant, find this acceleration.

plz help me to give a soln to it.

astarmathsandphysics:

--- Quote from: highly_ambitious on June 14, 2009, 09:44:01 am ---A cyclist is free-wheeling down a long straight hill. The times between passing successive kilometre posts are 100 seconds and 80 seconds. Assuming his acceleration is constant, find this acceleration.

plz help me to give a soln to it.

--- End quote ---

TIME TO TAVEL 1ST KM is 100s. If initial speed is u then from s=ut+1/2at2

1000=100u+5000a

time to travel the whole 2km is 180s s=ut+1/2at2

2000=180u+16200a

solving simulataneous equations gives u=155/18 m/s and a=1/36m/s2

highly_ambitious:
but the answer is [a=1/32 m/s/s]

astarmathsandphysics:
I think the markscheme must be wrong. I have checked it again and get the smae answer.

xcon89:

actually theres a little mistake that i spotted in your solution after solving myself, astar.

its that you have used 160 rather than 180 as the summed up time taken for 2000m distance.

BUT with that aswell the answer i am getting is 1/36 m/s^2
and not 1/32, maybe markscheme is wrong afterall -___-

lol

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