How Does Kinetic Energy Change in a Baseball After Being Hit?

In summary: No, don't tell your instructor to read that page. That page is actually written for instructors. You should just tell your instructor that you are having trouble solving the problems. ##In summary, the conversation discusses the kinetic energy and work done on a baseball after being hit, as well as the work done by air on the ball as it moves through the air. The kinetic energy and work calculations are solved for each scenario, and the concept of negative work is introduced. Additionally, a new question is added regarding determining the average force applied to a baseball by a bat, using the equation for work as the product of force and distance.
  • #1
Glenboro
39
0

Homework Statement


After being hit, a 0.145 kg baseball has a speed of 45.6 m/s.

1. What is the kinetic energy of the baseball after it has been hit?

2. How much work is done on the baseball by the baseball bat?

3. In moving through the air, the baseball slows down to a speed of 30.0 m/s. What work has the air done on the ball?

Homework Equations



K= (1/2)(m)v2
W= KEf-KEo[/B]

The Attempt at a Solution



1. KE = (1/2)(0.145kg)(45.6m/s)^2
KE = 150.75 J or 1.5 x 10^2J

2. W = 150.75J- 0J = 150.75J ( I assuming KEo is 0J since the kinetic energy of the baseball did not change even though its direction of motion is reversed)[/B]

3. W= KEf - KEo
W= (1/2)(0.145kg)(30.0m/s)^2 - 150.75j
W= 65.25 J - 150.75J
W = -85.5 J

I solved these 3 questions, but I don't think this isn't the right answers. Any criticism, advice or hint is appreciated.
 
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  • #2
If that is the entire question, those answers look correct (I didn't do the calculations but your work seems right). However, it seems like the problem might have given you an initial velocity before being hit, which would obviously change the second answer. As is, this is correct.
 
  • #3
mrnike992 said:
If that is the entire question, those answers look correct (I didn't do the calculations but your work seems right). However, it seems like the problem might have given you an initial velocity before being hit, which would obviously change the second answer. As is, this is correct.

Yeah, that was what the question was asking, it didn't give any initial velocity. Btw, for #3 can work be negative? I'm not sure if the work supposed to be positive or not.
 
  • #4
Glenboro said:
Yeah, that was what the question was asking, it didn't give any initial velocity. Btw, for #3 can work be negative? I'm not sure if the work supposed to be positive or not.
Yes, work can be negative.
 
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  • #5
jbriggs444 said:
Yes, work can be negative.
So, my answer in #3 is right ?
 
  • #6
Yes, it's correct.
 
  • #7
Glenboro said:
Yeah, that was what the question was asking, it didn't give any initial velocity.
You need to make an assumption about prior speed to answer the question. What seems more likely, that the speed was almost the same, or that it was so much less than after being struck that it can be taken as zero?
 
  • #8
haruspex said:
You need to make an assumption about prior speed to answer the question. What seems more likely, that the speed was almost the same, or that it was so much less than after being struck that it can be taken as zero?
I will add one more question on this questions

1)If the force of the baseball bat acts in the direction of the motion of the ball and the bat and ball are in contact for 0.0120 m, determine the average force applied to the baseball by the bat. In this case, the force of gravity can be ignored.

I'm having bit of trouble with this question, can you tell me which equation I should use?
 
  • #9
It looks like your instructor or textbook has fallen squarely into item 3 in one of our most recent Insights articles. https://www.physicsforums.com/insights/frequently-made-errors-mechanics-forces/

The intended approach in this case is for you compute the energy increase as work done. Work is the product of force times distance. If you know the energy and you know the distance [and if you are either casual or correctly careful about what is meant by "average"] then you can compute the average force.
 
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  • #10
jbriggs444 said:
It looks like your instructor or textbook has fallen squarely into item 3 in one of our most recent Insights articles. https://www.physicsforums.com/insights/frequently-made-errors-mechanics-forces/

The intended approach in this case is for you compute the energy increase as work done. Work is the product of force times distance. If you know the energy and you know the distance [and if you are either casual or correctly careful about what is meant by "average"] then you can compute the average force.
Then, should I tell my instructor to look at that page? Btw, thank you for explanation.
 

Related to How Does Kinetic Energy Change in a Baseball After Being Hit?

What is kinetic energy in baseball?

Kinetic energy in baseball refers to the energy that a baseball possesses due to its motion. This energy is a result of the baseball's mass and velocity.

How is kinetic energy calculated in baseball?

The formula for calculating kinetic energy in baseball is KE = 1/2mv^2, where m is the mass of the baseball and v is its velocity.

What factors affect the kinetic energy of a baseball?

The kinetic energy of a baseball can be affected by several factors, including the mass of the baseball, the velocity at which it is thrown or hit, air resistance, and the materials used in the construction of the baseball.

Why is kinetic energy important in baseball?

Kinetic energy is important in baseball because it determines the speed and distance at which the baseball will travel. It also plays a role in the power of a pitcher's throw and a batter's swing.

How does kinetic energy impact the game of baseball?

The amount of kinetic energy in a baseball can affect the outcome of a game, as it can determine the speed and trajectory of the ball. It can also impact the difficulty of catching and fielding the ball, as well as the distance a ball can travel when hit by a batter.

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