Newtons 2nd Law & Kinetics pt. 2

In summary, the problem involves a 500kg crate being pushed with a 2000N force, with a sliding friction force of 1900N acting on the crate. To find the net force, we must take into account the opposing direction of the friction force and add it to the pushing force, resulting in a net force of 100N. Using the equation a = \SigmaF/m, we can then calculate the acceleration, which is 0.2 m/s^2. With this acceleration, we can use the kinematic equations of motion to find the velocity and displacement of the crate after 10 seconds, resulting in a velocity of 2 m/s and a displacement of 10 meters.
  • #1
jtwitty
35
0

Homework Statement



A 500kg crate is pushed with a 2000N force. The force of the sliding friction acting on the crate is 1900N. How fast will the crate be moving after 10 seconds? How far will it have moved in this time? Determine the net force


Homework Equations



a = [tex]\Sigma[/tex]F/m



The Attempt at a Solution



I tried to find the new force by multiplying 500kg by 10 to get 5000N. Subtracted 5000n frmo 2000n. i don't think negative numbers can be a total force?

2000N-1900N = 100N. ? I don't know what that's used for
 
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  • #2
jtwitty said:

Homework Statement



A 500kg crate is pushed with a 2000N force. The force of the sliding friction acting on the crate is 1900N. How fast will the crate be moving after 10 seconds? How far will it have moved in this time? Determine the net force


Homework Equations



a = [tex]\Sigma[/tex]F/m



The Attempt at a Solution



I tried to find the new force by multiplying 500kg by 10 to get 5000N. Subtracted 5000n frmo 2000n. i don't think negative numbers can be a total force?

2000N-1900N = 100N. ? I don't know what that's used for

Why would you multiple mass by time to get a force?

You are given the two forces on the crate -- what is the "sum" of those forces? Be sure to include direction in the "sum".

And use your equation that you wrote a = [tex]\Sigma[/tex]F/m

to find the acceleration, which is what you need for the rest of the problem.
 
  • #3
berkeman said:
Why would you multiple mass by time to get a force?

You are given the two forces on the crate -- what is the "sum" of those forces? Be sure to include direction in the "sum".

And use your equation that you wrote a = [tex]\Sigma[/tex]F/m

to find the acceleration, which is what you need for the rest of the problem.

No i multiplied by 10 (gravity) (we round up frmo 9.8)
 
  • #4
jtwitty said:
No i multiplied by 10 (gravity) (we round up frmo 9.8)

You are not given the value of the coefficient of friction mu, so you cannot *calculate* the force of friction opposing the pushing motion. Guess you'll just have to figure out that force in a different way...

(Don't let the forest obscure your view of the trees...) :smile:
 
  • #5
i don't get what you;re saying hahahah

but ok back to the sum of the forces

2000 + 1900? = 3900

idk
 
  • #6
jtwitty said:
i don't get what you;re saying hahahah

but ok back to the sum of the forces

2000 + 1900? = 3900

idk

Much closer, but remember that the friction force opposes your pushing force. So if you are pushing with a force vector in the +x direction, what direction is the frictional force vector pointing in? And how do you "add" vectors?
 
  • #7
berkeman said:
Much closer, but remember that the friction force opposes your pushing force. So if you are pushing with a force vector in the +x direction, what direction is the frictional force vector pointing in? And how do you "add" vectors?
idk the word vector :cry:

but i think its pointing in a positive direction?
 
  • #8
jtwitty said:
idk the word vector :cry:

but i think its pointing in a positive direction?

A vector has magnitude and direction. When two vectors are pointing in opposite directions and you "add" them (like to sum the forces), the resultant vector is the difference in the magnitudes, and points in whichever direction the bigger vector pointed in the first place.

So if you are pushing with 2000N in the +x direction, and the crate's frictional force is pushing in the -x direction with 1900N, what is the resultant vector's magnitude and direction?

You can see the start of this introductory article if you need more info on how to add forces (vectors):

http://en.wikipedia.org/wiki/Vector_addition#Vector_addition_and_subtraction

.
 
  • #9
it would be poitning in the positive direction b/c its higher by 100N
 
  • #10
jtwitty said:
it would be poitning in the positive direction b/c its higher by 100N

Bingo! So now you know what the sum of the forces is. Use your equation to calculate the acceleration that results, and then just use the kinematic equations of motion (for constant acceleration) to solve the rest of the problem.
 
  • #11
berkeman said:
Bingo! So now you know what the sum of the forces is. Use your equation to calculate the acceleration that results, and then just use the kinematic equations of motion (for constant acceleration) to solve the rest of the problem.

so r u saying that 100N is the net force?

so a = 100 / 500

a = .2 m/s2
 
  • #12
help?
 
  • #13
jtwitty said:
help?

Help why? You are doing fine.
 
  • #14
berkeman said:
Help why? You are doing fine.

i didn't know if i was right or not :(

was i??
 
  • #15
a = .2m/s
d = 1/2 (.2) (100)
d = 10

a = vf /t
.2 = vf /10
2 = vf

done? :) how'd i do
 
  • #16
jtwitty said:
a = .2m/s
d = 1/2 (.2) (100)
d = 10

a = vf /t
.2 = vf /10
2 = vf

done? :) how'd i do

Looks good to me.
 
  • #17
ty man ty :)
 

What is Newton's 2nd Law?

Newton's 2nd Law, also known as the Law of Motion, states that the force applied to an object is equal to the mass of the object multiplied by its acceleration.

What is the equation for Newton's 2nd Law?

The equation for Newton's 2nd Law is F=ma, where F is the force applied to the object, m is the mass of the object, and a is the acceleration of the object.

How does Newton's 2nd Law relate to Kinetics?

Newton's 2nd Law is a fundamental principle in kinetics, as it describes the relationship between force, mass, and acceleration. It helps us understand how objects move and interact with each other.

What are some real-life examples of Newton's 2nd Law?

Some examples of Newton's 2nd Law in action are a car accelerating on a road, a ball being thrown, or a rocket launching into space. In each of these scenarios, there is a force applied to the object, causing it to accelerate.

How does Newton's 2nd Law differ from Newton's 1st Law?

Newton's 1st Law, also known as the Law of Inertia, states that an object at rest will remain at rest and an object in motion will remain in motion unless acted upon by an external force. This is different from Newton's 2nd Law, which specifically focuses on the relationship between force, mass, and acceleration.

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