Solving for Car's Acceleration, Time, and Average Speed

[Goopy17]

Homework Statement

A car is initial at rest. It accelerates over a distance of 1250m and reaches a speed of 112 km/h. Find: A) the acceleration for the car B) the time it took for it to reach this final speed C) the average speed

Homework Equations

A = delta V/ delta T or v^2 = V (initial)^2 + 2a (d -d(initial))
d = d(initial) + vt

The Attempt at a Solution

1250 = 0 + 31.1(t)
t = 40.18

A = 31.1/40.18
A = .77 m/s^2

BUT here is the problem

if i use v^2 = V (initial)^2 + 2a (d -d(initial))
31.1^2 = 0^2 + 2a(1250)
A = .387 m/s^2
that is half of the first one?


that is where i need help
Thanks!

 

[Ignea_unda]

if i use v^2 = V (initial)^2 + 2a (d -d(initial))
31.1^2 = 0^2 + 2a(1250)
A = .387 m/s^2
that is half of the first one?

Your solution for the acceleration in this section is correct.

1250 = 0 + 31.1(t)
t = 40.18

A = 31.1/40.18
A = .77 m/s^2

No.
Remember, the car is accelerating over this distance. It travels the 1250 meters before it reaches it's final speed.

Do you have the other equations of motion there? Which of them can you use that uses time and acceleration to compute a distance?

 

[Goopy17]

Not sure. Can you please explain?