Force and distance/velocity/acceleration

[jammhawk]

Homework Statement

A 2kg fan-cart is in linear motion (straight line on a very long track); it experiences 4N forward force due to the fan. Find the following assuming it is at rest initially:


a. The acceleration:
b. Its velocity 3 seconds after it starts
c. Its velocity 5 seconds after it starts
d. Its displacement between 3s and 5s
e. Its displacement between 0s and 5s
f. Its average velocity using the result from 4 for displacement

Homework Equations

The Attempt at a Solution

I know it sounds like a lot and I need A LOT of help. Our professor explained nothing and just handed this to us and said go. We don't even have a textbook, so help is really really needed. I am no where near being smart in physics.

 

[jammhawk]

Attempt
a.

a = F/m
a = 4N/2kg
a=4kg*m/ss/2kg

a=2m/s/s

Is that right?

 

[risk2112]

acceleration = net force / mass
acceleration = (final velocity - initial velocity) / timespan

displacement = (final V + initial V) \ 2) x timespan

With displacement, your initial velocity for "Its displacement between 3s and 5s" will not be 0.

*also acceleration is 2 m / s^2, and you need that to plug into all the equations i listed, and interpret what the questions r asking you to do

 

[jammhawk]

Can someone help me with a velocity formula? I keep looking for formulas but I can't really understand it.

 

[tiny-tim]

Welcome to PF!

Hi jammhawk! Welcome to PF!

Attempt
a.

a = F/m
a = 4N/2kg
a=4kg*m/ss/2kg

a=2m/s/s

Is that right?

Yes, that's fine.

In words, that means that the acceleration is constant.

You know some formulas for constant acceleration, don't you?

 

[jammhawk]

I have no clue what I am doing! I'm confused about all of this.

Ok.

I got
b. 6 m/s
c. 10 m/s
but i have no clue how i got it. and its probably wrong

 

[tiny-tim]

I have no clue what I am doing! I'm confused about all of this.

Ok.

I got
b. 6 m/s
c. 10 m/s
but i have no clue how i got it. and its probably wrong

Hi jammhawk!

Always show us how you got it (or how you think you got it)!

Hint: what formulas do you know that involve constant acceleration?

 

[jammhawk]

Basically in my head i said.
Aceleration = 2 m/s/s
Velocity = x m/s
so maybe V= at

 

[jammhawk]

And if those are true...

displacement = .5(a)(t^2) + vinitial(t) + dinitial

D = .5(2)(2^2) + 6(2) + 0
D = 4 + 12 + 0
D = 16

d. 16?

 

[tiny-tim]

Basically in my head i said.
Aceleration = 2 m/s/s
Velocity = x m/s
so maybe V= at

No maybe about it!

General formula v = u + at (and in this case u = 0).

And if those are true...

displacement = .5(a)(t^2) + vinitial(t) + dinitial

D = .5(2)(2^2) + 6(2) + 0
D = 4 + 12 + 0
D = 16

d. 16?

Also fine … excpet that you can scrub "+ dinitial" form the first line (though personally, I'd use vinitial = 0, and do two equations).

 

[jammhawk]

ok so all answers are good so far.

now how do i use the displacement of answer d (16) to find the average velocity?

 

[tiny-tim]

… now how do i use the displacement of answer d (16) to find the average velocity?

Definitions:

Speed = instantaneous distance-per-time

Average speed = total distance per total time. ​

 

[jammhawk]

so displacement = 16 meters
total time = 2 seconds

average velocity = 16 m/2s
8 m/s

right?

 

[tiny-tim]

so displacement = 16 meters
total time = 2 seconds

average velocity = 16 m/2s
8 m/s

right?

Yup!

btw:

Our professor explained nothing and just handed this to us and said go …

but your professor did tell you all the equations you've just used, didn't he?

Moral: physics is equations … just learn the equations, and practise choosing the right one to use. ​

 

[jammhawk]

actually i found all these online through yahoo. our professor gives us an assignment just sets us free. i wish he was more hands on

 

[tiny-tim]

actually i found all these online through yahoo. our professor gives us an assignment just sets us free. i wish he was more hands on

ah … then I sympathise …

web research is not a reliable way of learning physics.

 

[jammhawk]

i know... and I would like to thank you for the best help available!