# Work on a baseball being caught by a catcher

• Symon
In summary: The ball's kinetic energy decreases, so the work done on the ball is negative. The glove's kinetic energy increases, so the work done by the glove is positive.In summary, a baseball with a mass of 250g and a speed of 40m/s is caught by a catcher whose glove moves backward 0.25m while stopping the ball. The kinetic energy of the ball can be calculated using the equation Ek = 1/2(m)(v^2). The work done by the catcher's glove on the ball can be found using the equation Work = F x d x cos theta, where theta is the angle between the force and displacement vectors. The average stopping force on the ball can be determined by rearranging the work
Symon

## Homework Statement

A baseball of mass 250g (0.25kg), pitched with a speed of 40m/s, is caught by a catcher whose glove moves backward 0.25m while stopping the ball.

a) What is the kinetic energy of the ball? (solved)
b) How much work did the catcher's glove do on the ball?
c) What was the average stopping force on the ball?

Given: mass=0.25kg; speed=40m/s; distance=0.25m

Ek = 1/2(m)(v^2)
Work = F x d

## The Attempt at a Solution

I am completely stumped, I'm trying for the life of me to figure out how to find the Applied Force on the ball with what I've been given this unit. I'm not sure how to solve for the Force Applied without two of the other variables given for the work equation.

As for question C, what are they asking for? I'm unsure of what they mean by "stopping force".

If you are not familiar with the work-energy theorem, use the kinematic equations to solve for the deceleration of the ball, then apply Newton 2.

Is the theorem Work = Ekfinal - Ekinitial? If the initial kinetic energy = 5J, the final should be 0Jm because you're multiplying by 0 m/s. This gives me -5J which throws me off because I don't know if I should be taking the absolute value or not.

Symon said:
Is the theorem Work = Ekfinal - Ekinitial? If the initial kinetic energy = 5J, the final should be 0Jm because you're multiplying by 0 m/s. This gives me -5J which throws me off because I don't know if I should be taking the absolute value or not.
Work can be either positive or negative, depending on the direction of the force and the displacement.

Ah I understand, so when they ask for me to find "the average stopping force" are they asking me to re-arrange the W=F x d formula to solve for the force?

I'm really sorry about all the stupid questions I'm just trying to wrap my head around everything.

Symon said:
Ah I understand, so when they ask for me to find "the average stopping force" are they asking me to re-arrange the W=F x d formula to solve for the force?
Yes, but remember it's W=F x d x cos theta, where theta is the angle betwen the force and displacemnt vectors. What does the minus sign imply?

Does it imply a change in the displacement vector?

Symon said:
Does it imply a change in the displacement vector?
Imagine that I am the pitcher and you are the catcher. When you catch my pitched baseball, your glove moves (displaces) backward. Which way does the stopping force of your glove on the baseball act: forwards, or backwards? One of the keys to mastering Physics is mastering the plus and minus sign.

I would say the stopping force acts in the opposite direction that the ball is thrown, whilst the glove moves forewards in the same direction as the ball. Correct? Or have i gotten myself all backwards haha.

Symon said:
I would say the stopping force acts in the opposite direction that the ball is thrown, whilst the glove moves forewards in the same direction as the ball. Correct? Or have i gotten myself all backwards haha.
You've got it right.
That's why the work is negative.

## 1. How does a catcher catch a baseball?

A catcher catches a baseball by using their glove to secure the ball as it is thrown to them. They must also use their other hand to guide the glove and ensure the ball stays inside the glove.

## 2. What techniques do catchers use to catch a baseball?

Catchers use a variety of techniques to catch a baseball, including framing the pitch, blocking the ball with their body, and using their throwing hand to secure the ball in the glove.

## 3. How do catchers improve their catching skills?

Catchers improve their catching skills through practice, drills, and working with coaches to refine their techniques. They also study the tendencies of different pitchers and batters to better anticipate where the ball will be thrown.

## 4. What role does hand-eye coordination play in catching a baseball?

Hand-eye coordination is crucial for catchers, as they must be able to track the ball with their eyes and quickly react with their hands to catch it. Catchers with strong hand-eye coordination are often more successful at catching difficult pitches and preventing passed balls.

## 5. Is catching a baseball physically demanding?

Yes, catching a baseball can be physically demanding. Catchers must be in good physical shape to squat for long periods of time, as well as have strong arm muscles to make accurate throws to the infield. They also must be able to react quickly and move their body to catch pitches in different locations.

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