# Super Easy Question Im Sure

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 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

PhanthomJay
Homework Helper
Gold Member
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 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.)?

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