# Homework Help: Acceleration Problems

1. Jan 28, 2010

### christinacone

The first one is
It takes 40sec for a car at rest to reach a velocity of 50 m/s. What is the car's initial velocity?
a. 0 m/s
b. 1.25 m/s
c. 1.25 m/s2
d. 50 m/s
e. 50 m/s2
I think the equation is a=v(final)-v(intial)/t
but it can't be because doesn't a(acceleration)= m/s2?
so there for you don't have the number acceleration to plug in??
Also I think I think v(final) is 50 m/s... and I don't knbow but if something
is at rest then wouldn't that be v(intial)?? Please help!!!! I am so confused! OMG
I really need to know this for a upcoming test

The next one is.
It takes 40sec for a car at rest to reach a velocity of 50 m/s. What is the car's acceleration?
I know the answer for this one but what is confusing me is that I have to choices for this answer and they are
A. 1.25 m/s
B. 1.25 m/s2

could you explain to me which one is right and how did you come to get that
this is how I solved this problem

I used a=v(final)-v(initial)/t(time)
The v(final) is 50m/s and the v(initial) is 0 because the car started at rest.
and the t is 40 (because its in seconds
I subtracted 50-0 then divded it by 40.

Last but not least:
A car starts from rest has a constant acceleration of 4m/s2. In the first 3s the car travels
a. 6m
b. 12m
c. 18m
d. 172m
I really do not understand this one. Do you use the acceleration formula.

PLEASE HELP!! I went to tutoring at my university and they didn't know how to do them either! So help me smart people lol.

Thank you in advance!

2. Jan 29, 2010

### Lok

1. At rest means just that, this seems like a trick question but it isn't, you are supposed to know that without doubts. V=0

2. HINT! The International units of measure for acceleration are ... ?

3. The relevant formula is the acceleration formula x=Vinital*t+1/2a(tpower2) (t squared for all things.)
Again the initial speed is like in the first.

3. Jan 29, 2010

### Lok

Now i see you didn't understand the second m/s2 m/s

m/s means how many meters per second an object gains (travels). than means speed

m/s^2 means how much speed(m/s) per second an object gains (acceleration).

You used a formula. Maybe something like a=v/t well this means that a=m/s/s=m/s^2 (for best results keep in mind that v=m/s )