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Qualification => Subject Doubts => GCE AS & A2 Level => Sciences => Topic started by: highly_ambitious on July 28, 2009, 01:41:10 pm

Title: physics help!!!!!!!!
Post by: highly_ambitious on July 28, 2009, 01:41:10 pm
hey guys i need your help for some of the physics questions. I'm dumb in phy. so plzzz help me.

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

2. A train is slowing down with a constant deceleration. It passes a signal at A, and after successive intervals of 40 seconds it passes B and C, where AB = 1800m and BC=1400m. Find :
a. How fast is the train moving when it passes A?
b. How far from A does it come to stop?

I'll be very grateful to have the replies to the answers.so plz reply as soon as possible
Title: Re: physics help!!!!!!!!
Post by: astarmathsandphysics on July 28, 2009, 01:59:41 pm
Quote from: highly_ambitious on July 28, 2009, 01:41:10 pm
hey guys i need your help for some of the physics questions. I'm dumb in phy. so plzzz help me.

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

2. A train is slowing down with a constant deceleration. It passes a signal at A, and after successive intervals of 40 seconds it passes B and C, where AB = 1800m and BC=1400m. Find :
a. How fast is the train moving when it passes A?
b. How far from A does it come to stop?

I'll be very grateful to have the replies to the answers.so plz reply as soon as possible

1.Use suvat twice

s=1000
u=?
v=?
a=a
t=100

s=ut+1/2at2
1000=100u+5000a   (1)

s=2000
u=?
v=?
a=a
t=180

s=ut+1/2at2
2000=180u+16200a  (2)

Now solve (1) and (2) (2/412)-1.8(1) gives 200=7200a so a=1/36m/s2
Title: Re: physics help!!!!!!!!
Post by: astarmathsandphysics on July 28, 2009, 02:11:14 pm
2. A train is slowing down with a constant deceleration. It passes a signal at A, and after successive intervals of 40 seconds it passes B and C, where AB = 1800m and BC=1400m. Find :
a. How fast is the train moving when it passes A?
b. How far from A does it come to stop?

I'll be very grateful to have the replies to the answers.so plz reply as soon as possible

a)Use suvat twice again

For Ab

s=1800
u=u
a=a
v+?
t=40

s=ut+1/2at2

1800=40u+800a   (1)

For AC

s=3200
u=u
a=a
v+?
t=80

s=ut+1/2at2
3200=80u+3200a  (2)

(2)-2*(1) -400=1600a so a =-1/4m?s2

b)3200=80u+3200a from part a) and a=-1/4 so u=(3200-3200*-1/4)/80=50m/s

v2=u2+2as

0=502+2*-1/4*s so s=5000m




Title: Re: physics help!!!!!!!!
Post by: highly_ambitious on July 28, 2009, 03:07:31 pm
sir, but the answer is s=5000m .
Title: Re: physics help!!!!!!!!
Post by: astarmathsandphysics on July 28, 2009, 03:13:54 pm
I corrected the above p[ost