Finding the force of a person given mass.

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In summary: Ahhh I get it, you see the only example my professor gave in class was with an outside force pushing at an object, here there isn't any other force besides her weight, or mg pointing straight down! Thanks, my professor sucks at explaining things, thank you very much!
  • #1
mooney82
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Homework Statement



A 30-kg child on roller skates starts up a 10 degree incline at 15 km/h. Assuming she does not propel herself how far up the incline does she travel before stopping? Ignore frictional losses.


Homework Equations


F=ma W=mg

The Attempt at a Solution



I can do this problem if the force is given, but our book doesn't explain how to get force from mass, also would the 15 km/hr have anything to do with it? I've tried to work the problem out several times but I must be using the wrong value for force.
 
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  • #2
mooney82 said:
I can do this problem if the force is given, but our book doesn't explain how to get force from mass,
The force acting is the weight, which you should be able to calculate. What's the component of the weight parallel to the incline?
also would the 15 km/hr have anything to do with it?
The faster her initial speed, the longer it takes her to come to rest.
 
  • #3
So the weight is just m*g, which is 294.3 N?

The x component of mg would be 294.3cos10?
 
  • #4
mooney82 said:
So the weight is just m*g, which is 294.3 N?
Right.
The x component of mg would be 294.3cos10?
No, that's the component perpendicular to the incline (the y-component).
 
  • #5
Doc Al said:
Right.

No, that's the component perpendicular to the incline (the y-component).

But if i set the x-axis on the incline wouldn't the x component be the adjacent side?
 
  • #6
mooney82 said:
But if i set the x-axis on the incline wouldn't the x component be the adjacent side?
You need to understand how force components are found on inclined planes. Read: http://www.physicsclassroom.com/Class/vectors/u3l3e.cfm" [Broken]
 
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  • #7
Doc Al said:
You need to understand how force components are found on inclined planes. Read: http://www.physicsclassroom.com/Class/vectors/u3l3e.cfm" [Broken]

Ok, so does the force from the girl start parallel to the ground or the incline? I think that is where I might be getting it wrong. I've been setting it parallel to the ground.
 
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  • #8
mooney82 said:
Ok, so does the force from the girl start parallel to the ground or the incline? I think that is where I might be getting it wrong. I've been setting it parallel to the ground.
The weight acts downward--it has no horizontal component. Find the component parallel to the incline--that's the direction she's moving in.
 
  • #9
Doc Al said:
The weight acts downward--it has no horizontal component. Find the component parallel to the incline--that's the direction she's moving in.

Ahhh I get it, you see the only example my professor gave in class was with an outside force pushing at an object, here there isn't any other force besides her weight, or mg pointing straight down! Thanks, my professor sucks at explaining things, thank you very much!
 

1. How do you calculate the force of a person given their mass?

The force of a person can be calculated using the formula F=ma, where F is the force, m is the mass, and a is the acceleration.

2. What is the unit of measurement for force?

The unit of measurement for force is Newtons (N).

3. Can the force of a person change?

Yes, the force of a person can change depending on their mass and the acceleration they are experiencing.

4. How does the force of a person affect their surroundings?

The force of a person can affect their surroundings by causing objects to move or change direction, depending on the magnitude and direction of the force.

5. What factors can influence the force of a person?

The force of a person can be influenced by their mass, the surface they are standing on, and external forces such as gravity or friction.

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