Solving a Crate Motion Problem: Find Time for 4m Movement

In summary, the conversation discusses a problem involving a woman pushing a crate with a certain force and angle, and the weight and coefficient of kinetic friction of the crate. The conversation then goes through calculations to find the acceleration and time it takes for the crate to move a certain distance, but there is confusion about a certain step involving the frictional force.
  • #1
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Homework Statement



A woman pushes a crate with a force of 400N downward at a 35.2 angle down below horizontel. The crate weighs 300N. If coeffiecient of kenetic friction is 0.57, how much time does it take to move box 4m from rest.

Homework Equations



Fg=mg
Fk=(muk)mg

The Attempt at a Solution



I found fg by multiplying mass and gravity, I got 300N. Next I found Fk by multiplying micro by mass and gravity and got 171.1N.

Found gravity by doing 300/9.81 and got 30.6Kg.

Did

Fnety=Fn+Fay-Fg=0
0=Fn+400sin35.2-300
0=Fn+230.6-300
Fn=69.4

Fnetx=Fax-Fk
ma=Facostheta-Fk
30.6a=400cos35.2-171.1
30.6a=326.9-171.1
30.6a=155.9
a=5.1m/s2

Next i used d=V1t+.5at2
4=0t+.5(5.1)t2
4=2.55t2
t=1.57s

But I do not think I got the correct answer because I did not use the t2 after the 2.55 in anyway to find the answer. Did I do the rest of the work correct and just did the calculating of the time wrong, or is my other work wrong?

thanks!
 
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  • #2
I think the problem is with this part:

Fnetx=Fax-Fk
ma=Facostheta-Fk
30.6a=400cos35.2-171.1
30.6a=326.9-171.1
30.6a=155.9
a=5.1m/s2

Where does 171.1N come from? Normally frictional force is [tex]\mu F_N[/tex].
 
  • #3
Dont think so because I used the Fk= formula, and in the process I was trying to find Fn and I didnt know it so I used a different formula.

Fk=Ff

And Fk= muk x m x g

Fk= 0.57(30.6)(9.81)

I think it is in the ending but not sure, I just know the answer is wrong.
 

Related to Solving a Crate Motion Problem: Find Time for 4m Movement

What is a crate motion problem?

A crate motion problem involves determining the motion of a crate or object, typically in a straight line, given certain information such as distance, time, and velocity. It is a common type of problem in physics and engineering.

What is the goal of solving a crate motion problem?

The goal of solving a crate motion problem is to find the time it takes for an object to move a certain distance, given its initial velocity and any other relevant information. This can help in understanding and predicting the motion of objects in real-world situations.

What information is needed to solve a crate motion problem?

To solve a crate motion problem, you will need to know the distance the object is moving, its initial velocity, and any other relevant information such as acceleration or friction. It is important to have a clear understanding of the problem and what information is given before attempting to solve it.

What are the steps for solving a crate motion problem?

The general steps for solving a crate motion problem are as follows:1. Write down all given information and identify what is being asked for.2. Choose the appropriate formula to use based on the given information.3. Plug in the given values and solve for the unknown variable.4. Check your answer and make sure it makes sense in the context of the problem.5. If necessary, convert units to ensure consistency.

What are some common mistakes when solving a crate motion problem?

Some common mistakes when solving a crate motion problem include:- Using the wrong formula or equation- Not converting units correctly- Forgetting to include all relevant information- Making computation errorsIt is important to double check your work and make sure all steps are followed accurately to avoid these mistakes.

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