# Laws of motion HELP

Been struggling wih this problem all afternoon.

On an aircraft carrier, a jet can be catapulted fom 0 to 155 mi/hr in 2.00 sec. If the average force exerted by the catapult is 5.10 * 10^6 Newtons, what is he mass of the jet?

We converted the velocity into meters/second and got 69.276 meters/second

initial velocity = 0
initial X = 0
final X = (initial X) + (velocity of X)(time)
= 0 + 69.276(2.00)
= 138.6 meters

We don't know where to go from here...Summer classes. Test every Friday!!! NEED HELP ASAP!
Thanks

Write down everything the problem gives you.
F = 5.1 * 10^6 N
m = ?
$\Delta$V = 69.276m/s
$\Delta$t = 2s

What do you think comes next? You're trying to find M.

Pyrrhus
Homework Helper
Ok, you know a force made by the catapult produces an acceleration, so the jet will get from 0 to 155 in 2 seconds, you can find the acceleration (throught its definition) and then use Newton's 2nd Law.

That's too simple. If we were to use F=ma, acceleration would most likely be -9.8 m/s^2. then that would be 5.10 *10^6N/ -9.8m/s^2

But what is the time used for???
We were given this equation: X(final) = X(initial) + velocity of x * time + .5(acceleration)(time^2)

Where we are confused is we were never given an angle that it was catapulted, or a distance to go by, so we are stuck on this next step?!?

The formula was introduced earlier in the chapter, and it is something we have been using in other problems. I assume that is what we are supposed to be using.

Pyrrhus
Homework Helper
You believe the airplane doesn't run a horizontal trajectory before taking off?, This problem, indeed, has several simplifications, i imagine the purpose was what Whozum and i suggested.

You need to use the impuls equation which I hinted at already. Acceleration would not be 9.8m/s^, it would be 69.276/2 = 34.638m/s^2.

$$F\Delta t = m\Delta v$$

edit: clarificatoin

Newton's 2nd Law

$$F = ma$$

Average acceleration can be expressed as

$$a = \frac{\Delta v}{\Delta t}$$ which follows directly from it's definition. Plug that into the above to get what I just gave you.

Thank you so much! Really appreciate it...don't you hate when its staring you in the face :(