# Physics acceleration

1. Jan 28, 2005

### oldunion

A jet plane is cruising at 300 m/s when suddenly the pilot turns the engines up to full throttle. After traveling 4.0 km, the jet is moving with a speed of 400 m/s.

assuming a constant acceleration, what is it. answer is in m/s^2

I am not seeing how this is done without using time. also as a general question. i have no problem with math because it is logical and you have equations to solve it. but physics, i am constantly lost. am i to use known equations or do i have to make things up?

2. Jan 28, 2005

### cepheid

Staff Emeritus
I don't get it. Why would you just...make things up? They would be wrong.

In problems like this, always always always list the given quantities so that you know what information you have to work with. In this problem:

$$v_0 = 300 \text{m/s}$$

$$v = 400 \text{m/s}$$

$$d = 4000 \text{m}$$

$$a = \text{const.}$$

Now, ask yourself: I have the initial and final velocities, the acceleration (to solve for), and the distance travelled. For motion in a straight line with constant acceleration, is there some relationship that relates these quantities? The answer should be a resounding yes. You have no doubt derived in class a kinematical formula expressing the final velocity in terms of the initial velocity, acceleration, and the distance travelled (over the course of that change in velocity).

3. Jan 28, 2005

### oldunion

haha, im afraid you have the idea of my class all wrong. he will look at this projector the whole time and personally do 2 or 3 problems leaving everyone clueless. thus, i learn physics from this book im looking at and a workbook. so im teaching myself more or less.

i have (400m/s)^2=(300m/s)^2+2a4000

a=8.75m/s^2 correct?

Last edited: Jan 28, 2005
4. Jan 28, 2005

### vincentchan

what did you mean...are you saying the answer is what you just said.....
you and cepheid are completely correct

5. Jan 28, 2005

### oldunion

i was guessing, is the answer (8.75m/s)^2?

6. Jan 28, 2005

### vincentchan

did I tell you that you and cepheid is completely correct?????

7. Jan 28, 2005

### oldunion

yes, but i dont see my answer quoted. thank you for your help