# Physics with cal 1 probs

#### Zandorian

If you guys can help me with this I would appreciate it.

1. A passenger plane lands with a speed of 98m/s and accelerates at -7.0m/(s^2). After how many s does it come to rest?

2. A train moving at 32.0 m/s brakes to a stop in 22.0 s. How far in m did it move while coming to a stop?

3. A rock is thrown upward with a speed of 23m/s. What maximum height in m does it reach before falling back to earth?

I need to know how to do these problems as well as the answers.

Thanks

Related Introductory Physics Homework Help News on Phys.org

#### HallsofIvy

Homework Helper
First you need to know some basic definitions: How is "acceleration" DEFINED?

Do you know any formulas connecting distance and acceleration?

#### Zandorian

avg or inst Accel?

no, dont think so

#### amcavoy

v=at+v0

You have your initial velocity (v0) and your acceleration. You want to see how many seconds it will take for the plane to stop. That is, how long will it take until v=0? I think you can do the rest...

Also:

s=.5at2+v0t+s0

Last edited:

#### Zandorian

no, i can't.

do i need to find the inst acc and inst vel at v0?

#### amcavoy

v0 is the speed that the train is moving at when it begins to brake.

#### Zandorian

apmcavoy said:
v0 is the speed that the train is moving at when it begins to brake.
TRAIN, i thought u were heliping me with the 1st one. lol

#### Zandorian

anyone want to give me the complete solution to the first or second problem?

#### Zandorian

i really need help here guys.................i don't under stand what I am supposed to plug into the equation. I see them in my textbook, but I dont understand what the stand for

#### Tom Mattson

Staff Emeritus
Gold Member
Zandorian said:
anyone want to give me the complete solution to the first or second problem?
We don't do that here. You are supposed to show how you started and where you got stuck, and then we help you, not do it for you.

#### Tom Mattson

Staff Emeritus
Gold Member
Zandorian said:
I just want you to explain it not do it for me.
Then why did you ask for a complete solution?

Look, give it a shot and see what you come up with. You've got a short list of kinematical equations in your book (which you have read, right?). You should be able to at least try to figure out what the given information is (time, acceleration, initial velocity, etc...) and figure out what the unknown is for each part. Then you can search your list of equations for the correct one that relates what you've been given to what is being asked for. There will only be one in each instance.

#### amcavoy

Zandorian said:
TRAIN, i thought u were heliping me with the 1st one. lol
I was referring to the second one, but the same holds true for the plane when it lands...

#### Zandorian

Tom Mattson said:
Then why did you ask for a complete solution?

Look, give it a shot and see what you come up with. You've got a short list of kinematical equations in your book (which you have read, right?). You should be able to at least try to figure out what the given information is (time, acceleration, initial velocity, etc...) and figure out what the unknown is for each part. Then you can search your list of equations for the correct one that relates what you've been given to what is being asked for. There will only be one in each instance.

I dont understand WHAT they stand for
just tell me what they stand for

#### Tom Mattson

Staff Emeritus
Gold Member
a=acceleration
vf= final velocity
vi=initial velocity
xf=final position
xi=initial position
t=time

#### Zandorian

IS THE ANswer 14???? to the 1st one

#### Tom Mattson

Staff Emeritus
Gold Member
Yes, it is. Just don't forget that the answer includes its units.

### Physics Forums Values

We Value Quality
• Topics based on mainstream science
• Proper English grammar and spelling
We Value Civility
• Positive and compassionate attitudes
• Patience while debating
We Value Productivity
• Disciplined to remain on-topic
• Recognition of own weaknesses
• Solo and co-op problem solving