[JonathanEyoon]

If an object is accelerating at a rate of 25 m/s2, how long (in seconds) will it take to reach a speed of 550 m/s? (Assume an initial velocity of zero.)





I don't expect anyone to give me the answer but rather I want to figure it out =) Can someone lead me in the right direction? Thanks

[Alpha-Omega]

a =(v_f – v_i)/t

t =(v_f – v_i)/a

V_i = 0
V_f = 550 m/s
a = 25 m/s²

remeber to keep track of the units....you have m/s in the numerator and m/s² in the denominator and yiou will be left with seconds.

[JonathanEyoon]

oh wow that really confused me a bit more

[Alpha-Omega]

your formual is acceleration = Vfinal - Vinitial/t

you have some algebra to do:

a = (Vf -vi)/t

t = (vf - vi)/a

s = (m/s -m/s)/(m/s²)

so

s = (m/s - m/s) x s²/m

Do you know that  dividing by m/s²  is the same as multiplying by the inverse?

[Alpha-Omega]

This is a physics equation.

a = (v_f - v_i)t    is your basic equation for acceleration

This equation states:  acceleration is equal to the change in velocity (v_f - v_i) divided by the time.


V_f = final velocity = 550 m/s GIVEN
v_i = initial velocity = 0 m/s GIVEN
a = acceleration = 25 m/s² GIVEN

So you need to isolate t and solve for t .  t is the time.

Easiest way to solve this is to just rarrange the equation to isolate t and then plg in your numbers...

a = (v_f - v_i)t

t = (v_f - v_i)/a

then plug in the numbers and solve for t

[JonathanEyoon]

  


My chemistry teacher assigned these problems as conversion problems. Eek!! Why is she giving us physics problem?

[enahs]

It is still basic algebra and the math applies to chemistry.

mebecker's way of working it applies the laws of physics. It can be done by just looking at the units as your teacher was getting at.

You have a unit of m/s² and of m/s, and you want to end with just seconds?
How do you do that?

Hint: It is the same as the next to last line in mebeckers previous post to verify your answer.

[JonathanEyoon]

ok the answer is 22 to the question.  Now I don't know how it's 22

[Alpha-Omega]

This is how:

t = (550 m/s - 0 m/s)/25 m/s²

so:

(550 m/s)/(25 m/s²) = 22 s

then: 550/25 = 22

and your units are: (m/s )/(m/s²) = s

Thus:  22 s

I know you are learning conversions....but the statement of your probem: 

If an object is accelerating at a rate of 25 m/s², how long (in seconds) will it take to reach a speed of 550 m/s? (Assume an initial velocity of zero.)

EXACTLY the same as what I taught my HS students in HS physics. You will see this in conversions and in equations of motion.

[enahs]

ok the answer is 22 to the question.  Now I don't know how it's 22

How your teacher wanted you to work it.

550 m   *    1 s²     = 22 s
      s          25 m


If you wish to learn more about what mebecker said (which you should, it is good stuff and you will have to learn it in college at the latest, if not later in your high-school career), when you have time peruse this site and its animations and read and such.
http://www.physicsclassroom.com/Class/1DKin/U1L1e.html

[Alpha-Omega]

Maybe this will help:

Acceleration = a = m/s²
Velocity (speed) = v = m/s  (and I do not like that speed and velocity are NOT the same thing)
Time = t = s