How Many Rocks Must a Child Throw to Maintain Constant Speed in a Wagon?

AI Thread Summary
To maintain a constant speed in the wagon against a 3.5 N frictional force, the child must exert an equal force through the momentum change from throwing rocks. Each rock, weighing 0.47 kg and thrown at 9 m/s, contributes to the overall momentum. The necessary force can be calculated using Newton's second law, which relates force to the rate of change of momentum. By determining the required force and the momentum change per thrown rock, the number of rocks thrown per minute can be calculated. Understanding these principles is essential for solving the problem effectively.
bkoz316
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Remain at constant speed?

A child sits in a wagon with a pile of 0.47 kg rocks. If she can throw each rock with a speed of 9 m/s relative to the ground, causing the wagon to move, how many rocks must she throw per minute to maintain a constant average speed against a 3.5 N force of friction?



Not sure on what to do...please help!


Thanks!
 
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bkoz316 said:
A child sits in a wagon with a pile of 0.47 kg rocks. If she can throw each rock with a speed of 9 m/s relative to the ground, causing the wagon to move, how many rocks must she throw per minute to maintain a constant average speed against a 3.5 N force of friction?



Not sure on what to do...please help!


Thanks!
You have to determine what force the child must exert the wagon in order to make it move at constant speed. Then that force can be equated to the momentum change caused by the changing mass (Hint: F= rate of change of momentum, per Newton's 2nd law).
 

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