Shouldn't these equations produce the same result?

[Breadsticks]

Homework Statement

If a pilot accelerates at more than 4g, he begins to “gray out” but doesn’t completely lose consciousness. (a) Assuming constant acceleration, what is the shortest time that a jet pilot starting from rest can take to reach Mach 4 (four times the speed of sound) without graying out? (b) How far would the plane travel during this period of acceleration? (Use 331 m s for the speed of sound in cold air.)

Homework Equations

2aΔx=V²-V₀²
Δx=V₀t+(1/2)at²

The Attempt at a Solution

I was reviewing my work for the chapter and came across a problem with part b. I used 2aΔx=V²-V₀² instead of Δx=V₀t+(1/2)at² like I did the first time. The time it takes is 33.7 seconds, and initial velocity is zero with final velocity being 1324 m/s. The acceleration is 39.24 m/s². Using the second equation, I get the right answer of 22392 m. But using the first equation, I get 2087 m. Why is this? If there is a final velocity and an initial velocity, and acceleration is the same with both, wouldn't it have to take the same time?

 

[ehild]

Homework Statement

If a pilot accelerates at more than 4g, he begins to “gray out” but doesn’t completely lose consciousness. (a) Assuming constant acceleration, what is the shortest time that a jet pilot starting from rest can take to reach Mach 4 (four times the speed of sound) without graying out? (b) How far would the plane travel during this period of acceleration? (Use 331 m s for the speed of sound in cold air.)

Homework Equations

2aΔx=V²-V₀²
Δx=V₀t+(1/2)at²

The Attempt at a Solution

I was reviewing my work for the chapter and came across a problem with part b. I used 2aΔx=V²-V₀² instead of Δx=V₀t+(1/2)at² like I did the first time. The time it takes is 33.7 seconds, and initial velocity is zero with final velocity being 1324 m/s. The acceleration is 39.24 m/s². Using the second equation, I get the right answer of 22392 m. But using the first equation, I get 2087 m. Why is this? If there is a final velocity and an initial velocity, and acceleration is the same with both, wouldn't it have to take the same time?

You certainly miscalculated something. Both method gives the same result.