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Qualification => Subject Doubts => GCE AS & A2 Level => Sciences => Topic started by: highly_ambitious on June 14, 2009, 09:44:01 am

Title: need help. physics question.
Post by: 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.
Title: Re: need help. physics question.
Post by: astarmathsandphysics on June 14, 2009, 10:15:46 am
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.

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
Title: Re: need help. physics question.
Post by: highly_ambitious on June 14, 2009, 10:24:24 am
but the answer is [a=1/32 m/s/s]
Title: Re: need help. physics question.
Post by: astarmathsandphysics on June 14, 2009, 10:37:26 am
I think the markscheme must be wrong. I have checked it again and get the smae answer.
Title: Re: need help. physics question.
Post by: xcon89 on June 15, 2009, 06:04:01 pm

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
Title: Re: need help. physics question.
Post by: astarmathsandphysics on June 15, 2009, 07:13:48 pm
You are right I misread the question. I corrected my post.