Super Easy Question Im Sure

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A child sits in a wagon with a pile of 0.59 kg rocks. If she can throw each rock with a speed of 10 m/s relative to the ground, how many rocks must she throw per minute to maintain a constant average speed against a 2.8 N force of friction?

I know this question is probably increadibly easy...its listed as an easy problem in the book...but it is not clicking.

I believe I have to use the thrust = (delta m/delta t) x v but I think I am setting it up wrong.

I had 2.8 as the thrust as this is the amount of force needed to keep an average speed so

2.8 = (0.59/x) x 10
which leads to 5.9/2.8
which equals 2.1 seconds in time....

If this first part is correct, then i am having trouble converting this time into amount of rocks.

I suspect I set the first part up wrong though
 

Answers and Replies

  • #2
PhanthomJay
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A child sits in a wagon with a pile of 0.59 kg rocks. If she can throw each rock with a speed of 10 m/s relative to the ground, how many rocks must she throw per minute to maintain a constant average speed against a 2.8 N force of friction?

I know this question is probably increadibly easy...its listed as an easy problem in the book...but it is not clicking.

I believe I have to use the thrust = (delta m/delta t) x v but I think I am setting it up wrong.

I had 2.8 as the thrust as this is the amount of force needed to keep an average speed so

2.8 = (0.59/x) x 10
which leads to 5.9/2.8
which equals 2.1 seconds in time....

If this first part is correct, then i am having trouble converting this time into amount of rocks.

I suspect I set the first part up wrong though
I seldom find any physics problem incredibly easy. You just made it look easy. One rock every 2.1 seconds is how many rocks in 60 seconds (no fractions, please.)?
 
  • #3
41
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Wow...I can do all the hard work...its the little things that get me lol

Thanks for pointing out that obvious thing...

Giving a final answer of 28

Thanks again sir
 

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