Solving the Friction Wagon Homework Problem

[homevolend]

Homework Statement

A wagon friction fore is 60N when moving, same for any load its carrying. A horizontal force is applied of 150N causes wagon to be accerate at 5 m/s/s. The same force with a child in the wagon causes it to accerate at 1 m/s/s how do I answer this question to find mass of the child?

Homework Equations

M = F/A

The Attempt at a Solution

First I don't know to find the F in the above equation. I tried doing 150-60 got me 90. So I did the 90/1. Which is 90 kg. But I don't think I did this question correctly as I didnt use 5 at all and the mass of a child cannot be 90 kg. Did I answer it right?


Thanks!

 

[collinsmark]

A wagon friction fore is 60N when moving, same for any load its carrying. A horizontal force is applied of 150N causes wagon to be accerate at 5 m/s/s. The same force with a child in the wagon causes it to accerate at 1 m/s/s how do I answer this question to find mass of the child?
[...]
I tried doing 150-60 got me 90. So I did the 90/1. Which is 90 kg.

What, in all, is accelerating in this situation (where the acceleration is 1 [m/s²])? Is it just the child, or the wagon+child?

What's the mass of the wagon?

 

[PhanthomJay]

Homework Statement

A wagon friction fore is 60N when moving, same for any load its carrying. A horizontal force is applied of 150N causes wagon to be accerate at 5 m/s/s. The same force with a child in the wagon causes it to accerate at 1 m/s/s how do I answer this question to find mass of the child?

Homework Equations

M = F/A

The Attempt at a Solution

First I don't know to find the F in the above equation. I tried doing 150-60 got me 90.

Yes, that is the NET force, in Newtons.

So I did the 90/1. Which is 90 kg. But I don't think I did this question correctly as I didnt use 5 at all

you should have, instead of using 1. That gives you the mass of the wagon

and the mass of a child cannot be 90 kg. Did I answer it right?


Thanks!

Once you solve for the mass of the wagon, use Newton's 2nd law with the child's mass (M) combined with wagon's mass, to solve for the child's mass.

EDIT: collinsmark beat me to it as I was responding.!

 

[homevolend]

The 1.0 m/s/s is wagon+child. I have found the mass now of just the wagon. Now to find the mass of the child alone do I take the Fnet and divide it by 1 ? As 1 is the acceration.

 

[collinsmark]

The 1.0 m/s/s is wagon+child. I have found the mass now of just the wagon. Now to find the mass of the child alone do I take the Fnet and divide it by 1 ? As 1 is the acceration.

Well, if you already know the mass of the wagon+child (together), and you already know the mass of the wagon (by itself), the mass of the child must be ...

 

[homevolend]

I do not know what it is with the wagon + child together though. I just know what the mass of the wagon by itself is.

 

[collinsmark]

I do not know what it is with the wagon + child together though. I just know what the mass of the wagon by itself is.

In the case where the wagon is accelerating at 1 [m/s²], the total mass is (mass of wagon + mass of child)

Use Newton's second law to find the mass of wagon+child.

In the case where the wagon is accelerating at 5 [m/s²], the total mass is only the mass of the wagon. You can use Newton's second law again here to find the mass of the wagon.

 

[homevolend]

K=60N 150-60 = 90N which is the Fnet.
Fa=150N 90/5= 18kg wagon
a1=5m/s/s 90/1= 90kg wagon+child
a2=1 m/s/s

90
- ----- = 72kg child
18

Thanks for helping me answer this question, I guess I didn't fully understand it.

I appreciate it collinsmark