What is Bob's maximum power output as he throws the rock?

In summary, Bob is able to throw a 500 g rock with a speed of 30 m/s by applying a force of 225 N and doing 225 J of work on the rock. His maximum power output is 6750 W. The problem can also be solved using work-energy methods, where the equation KE = work times distance is used and the work done by Bob can be calculated by setting delta E = 0 and solving for Wext. This method yields the same results as using Newton's second law.
  • #1
habibclan
55
0

Homework Statement


Bob can throw a 500 g rock with a speed of 30 m/s. He moves his hand forward 1.0 m while doing so.
a. How much work does Bob do on the rock?
b. How much force, assumed to be constant, does Bob apply to the rock?
c. What is Bob's maximum power output as he throws the rock?


Homework Equations


vf^2= vi^2 + 2ad
F=ma
W= F.d

P= F.v

The Attempt at a Solution



Find the acceration provided by the applied force.

vf^2= vi^2 + 2ad
30^2= 2a (1)
a= 450 m/s^2

Then find the force using Newton's second law:
F=ma
F= 450 (0.5)
F= 225 N

Now calculate work using the force applied.

W= F.d
W= 225 *1= 225 J

Power= F.v= 225*30= 6750 W.

Is this the correct way to do it? my textbook doesn't have solutions to even-numbered problems and I'm not sure if my way of calculating acceleration and then using Newton's second law is correct. Any help would be greatly appreciated!
 
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  • #2
That looks just fine. You could have done it perhaps a bit quicker using work-energy methods (if you are familiar with this method), but there's always more than one way to attack a problem.
 
  • #3
PhanthomJay said:
That looks just fine. You could have done it perhaps a bit quicker using work-energy methods (if you are familiar with this method), but there's always more than one way to attack a problem.

We apparently covered this method but the only work-energy equation that I know is: Ki+ Ui + Wext= Kf+ Uf+ delta E (thermal). Can you please guide me on how to set it up the work-energy way because I've seen other questions in the textbooks like that but I do them different.Thanks for your help =).
 
  • #4
habibclan said:
We apparently covered this method but the only work-energy equation that I know is: Ki+ Ui + Wext= Kf+ Uf+ delta E (thermal). Can you please guide me on how to set it up the work-energy way because I've seen other questions in the textbooks like that but I do them different.Thanks for your help =).

Hi habibclan! :smile:

Just put delta E = 0.

So in this case the equation is KE = work times distance.

Try it! :smile:
 
  • #5
tiny-tim said:
Hi habibclan! :smile:

Just put delta E = 0.

So in this case the equation is KE = work times distance.

Try it! :smile:

But I don't know work. I still don't get it :(.
 
  • #6
habibclan said:
We apparently covered this method but the only work-energy equation that I know is: Ki+ Ui + Wext= Kf+ Uf+ delta E (thermal). Can you please guide me on how to set it up the work-energy way because I've seen other questions in the textbooks like that but I do them different.Thanks for your help =).
As tiny-tim noted, delta E =0. So using your equation, 0 + 0 + Wext = 1/2mv^2 + 0 + 0. You know v=30, and m= .5, solve for Wext (the work done by Bob on the rock). Then since Wext = Fd, solve for F.
 
  • #7
Thanks a lot tiny-tim and PhantomJay! The help is much appreciated!
 

1. What is meant by "maximum power output"?

The maximum power output refers to the amount of energy that Bob is able to transfer to the rock as he throws it. It is the highest amount of energy that he can generate and is usually measured in watts.

2. How is Bob's maximum power output calculated?

Bob's maximum power output can be calculated by dividing the work he does on the rock by the time it takes him to throw it. This can be measured using a variety of scientific tools, such as force plates or motion sensors.

3. What factors affect Bob's maximum power output?

Several factors can affect Bob's maximum power output, including his muscle strength, body weight, technique, and the weight and size of the rock. Other factors, such as air resistance and friction, may also play a role.

4. How can Bob increase his maximum power output?

Bob can increase his maximum power output by improving his muscle strength and technique through regular training and practice. He can also optimize his body position and use proper throwing mechanics to generate more force behind his throw.

5. Why is it important to know Bob's maximum power output when throwing a rock?

Knowing Bob's maximum power output can help us understand his physical capabilities and limitations when throwing a rock. It can also help us determine the best approach and technique for Bob to use in order to achieve maximum distance and accuracy in his throws.

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