Opted Physics Question #10

[giggles86]

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I was wondering if anyone could explain how to arrive at correct answer for the Opted physics question #10?

The question states:
A 50-kg girl pulls a 20-kg wagon with a force
of 10 Newtons. The wagon accelerates at
2 m/s2. What is the force, in Newtons, exerted
BY the wagon ON the girl?

The answer is 10N, but I don't know how to go about doing the problem.
Thank you!

 

[Rusty Ryan]

I think its 10 N because of Newton's 3rd Law (Action-Reaction forces).

 

[giggles86]

Thanks! That's what I figured, just wanted to make sure there wasn't something tricky I was missing

 

[EyEnStein 07]

It is 10N because of the 3rd law, and you can even see that if you draw out body diagrams....but i dont see how the wagons a works out to be 2 m/s^2...i know its given but if you think about it with a 10N force the girl accelerates about .2m/s^2.....so that should mean the wagon is accelerating at .5m/s^2 ...wierd unless im missing something.

 

[NatashaColorado]

It is 10N because of the 3rd law, and you can even see that if you draw out body diagrams....but i dont see how the wagons a works out to be 2 m/s^2...i know its given but if you think about it with a 10N force the girl accelerates about .2m/s^2.....so that should mean the wagon is accelerating at .5m/s^2 ...wierd unless im missing something.

You are right, it doesn't work if you use F = ma. 10N is not equal 20kg x 2m/s^2. Either mass had to be 5 kg or acceleration 0.5m/s^2