Question

physics,
can someone help me solve part b of this problem


https://www.dropbox.com/s/8uwrpl0h3fcm1r8/Screenshot%202015-12-13%2018.58.35.png?dl=0

Answer 1

what did you get for part A?

Answer 2

using
v= a*t
and
d= 0.5 a * t^2
then
d/v = 0.5t
and
t= 2d/v
where d is distance traveled and v is the final velocity

Answer 3

after distance d, there is 100-d still to go, at velocity 11

thus the total time to run the race is
2d/v + (100-d)/v = 10 seconds

here v is 11
and we want to solve for d

Answer 4

@phi for a i got 13

Answer 5

13,04 seconds

Answer 6

How?

Answer 7

i used kinematic equations

Answer 8

can you post them? I get a different result for A

Answer 9

sec

Answer 10

https://www.dropbox.com/s/wy2orousogw0od7/Screenshot%202015-12-14%2014.48.58.png?dl=0

Answer 11

that all looks ok, except I don't see how you get 13 seconds
isn't it 24/11 seconds to accelerate to 11 m/s^2 and 8 seconds to complete the race?
that adds up to 10 2/11

Answer 12

you must have added the acceleration (5.04) to 8 seconds to get 13.04
you want to use the time
V= a * t
11 = 121/24 * t
t= 24*11/121 = 24/11 = 2 and 2/11

Answer 13

10,18 seconds ?

Answer 14

We know the initial velocity and distance are zero, so the equations simplify to just
\[ v_f = a t \\ x= \frac{1}{2} a t^2 \]
or
\[ 2x= a t^2\\ v_f= a t\]
if we divide the equations (i.e. divide the left sides and right sides) we get
\[ \frac{2x}{v_f}= t \]

we are told x is 12 m and v_final = 11 m/s^2 so we find
\[ \frac{2\cdot 12}{11}= t \\ t= \frac{24}{11} = 2.1818...\]

and total time is 8 + 2.1818= 10.1818...

Answer 15

For part B, we can use that same equation for the time to accelerate to v_final
\[ t_1= \frac{2x}{11} \]
and the time to complete the race is
\[ t_2= \frac{100-x}{11} \]
and the total time is
\[ t_1+t_2= 10 \]

Answer 16

i see

Answer 17

You can finish the problem?

Answer 18

I think I can yes

Answer 19

(x1 - 0 + x2 - x1) / 11

Answer 20

what is x2?

Answer 21

to find the distance x in Part B , the equation is
\[ \frac{2x}{11}+ \frac{100-x}{11} = 10 \\
2x + 100 -x = 110 \\
x+100 = 110\\
x= 10\]