Physics Help

Finding this question really hard
A rail wagon moving at a speed on a level track reached a steady incline which slowed it down to rest in 15.0s and caused it to reverse. Calculate
its velocity and position on the incline after 20.0s
( i already found the distance moved up which is 15m and the acceleration is -1.3ms-2)

Thanks :biggrin:

Reply 1

OP

bump

How did you calculate those values of distance and deceleration?
The question you have written doesn't have enough information to do that.
You have given us final velocity = 0 and time = 15s
This is only 2 out of the 3 needed for a suvat equation.

If your answer for distance moved up the slope is 15m then the initial velocity had to be 2m/s
This gives an acceleration of -2/15 = -0.13m/s/s

Can you check that
a) you have written the question exactly as it is in the book/exam
b) your calculations for s and a

Reply 3

avtar95

OP

6

Original post by Stonebridge

How did you calculate those values of distance and deceleration?
The question you have written doesn't have enough information to do that.
You have given us final velocity = 0 and time = 15s
This is only 2 out of the 3 needed for a suvat equation.

If your answer for distance moved up the slope is 15m then the initial velocity had to be 2m/s
This gives an acceleration of -2/15 = -0.13m/s/s

Can you check that
a) you have written the question exactly as it is in the book/exam
b) your calculations for s and a

my bad
A rail wagon moving at a speed of 2.0ms-1 on a level track reached a steady incline which slowed it down to rest in 15.0s and caused it to reverse.
To find the distance it moved up i did
s=1/2(u+v)t
and to find acceleration s=ut+1/2at2
but I can't find it's velocity and position on the incline after 20.0s

Reply 4

Stonebridge

13

Just put t= 20s into the suvat equations with
u=2m/s
a=-0.133m/s/s
t=20s

to find v and s
v will be negative because it's coming back down the slope.
s will be less than 15m because it is now nearer the bottom of the slope.
Make sure a is negative as it is also in the direction down the slope
u is positive as it is up the slope.
Keep the signs in order and you will get the answer. The maths will take care of it.

(edited 12 years ago)

Reply 5

avtar95

OP

6

Original post by Stonebridge

Just put t= 20s into the suvat equations with
u=2m/s
a=-1.3m/s/s
t=20s

to find v and s
v will be negative because it's coming back down the slope.
s will be less than 15m because it is now nearer the bottom of the slope.
Make sure a is negative as it is also in the direction down the slope
u is positive as it is up the slope.
Keep the signs in order and you will get the answer. The maths will take care of it.