# How Is Impulse Calculated in a Baseball Pitch?

• master_333
In summary: You could just as well write FΔt = Δp. Δp is the change in momentum. So to find impulse, just use the change in momentum.In summary, the conversation discusses a problem involving a baseball being hit by a bat and the magnitude of the impulse and average force exerted by the bat on the ball. After some confusion about the direction of the impulse, it is determined that the correct approach is to use the change in momentum to find the impulse and average force. The final answer for the total impulse is 90 kg*m/s.
master_333

## Homework Statement

A 0.150-kg baseball, thrown with a speed of 40.0 m/s, is hit straight back at the pitcher with a speed of
50.0 m/s. (a) What is the magnitude of the impulse delivered by the bat to the baseball? (b) Find the magnitude of the average force exerted by the bat on the ball if the two are in contact for 2.00 * 10 ^-3 s.

## Homework Equations

I = change in momemtum

## The Attempt at a Solution

I don't know why doing it this way works out.

I = (0.150kg)(40m/s)
I = 6 kg*m/s

I = (0.150kg)(50m/s)
I = 7.5 kg*m/s

I (total) = 6 + 7.5 = 13.5 kg*m/s

Well yes you get the right answer but your approach isn't right, you made two mistakes, but it got you to the right answer :-)
Firstly label your attempt with I1 and I2
Your I1 value is perfect if you assume your positive axis towards the batsman
That being said, do you think your I2 value is right?(consider the direction)

Suraj M said:
That being said, do you think your I2 value is right?(consider the direction)
I don't see a problem there, necessarily. It depends on exactly what master_333 was thinking.
Both velocity numbers in the calculation (40m/s, 50m/s) can be read as changes in velocity measured in the batter to pitcher direction, the first to halt the ball and the second to return it. The corresponding impulses therefore have the same sign and should be added.

Sorry I took I as momentum,
So I thought ##I_2## should be negative, that's the way we were taught to do it
Sorry I was wrong,:-/

Suraj M said:
Sorry I took I as momentum,
So I thought ##I_2## should be negative, that's the way we were taught to do it
Sorry I was wrong,:-/
Yes, I is momentum.
Here are two methods, both valid. In both cases, I will take the positive direction as batter to pitcher:
1.
Initial momentum of ball = m(-40m/s)=-40m m/s.
Final momentum of ball = m(50m/s) = 50m m/s.
Change = 50m-(-40m) = 90m.

2.
Momentum needed to stop ball = 40m
Momentum needed to return stationary ball = 50m
Total needed = 90m.

Since master_333 was surprised his method worked, it is unclear whether method 2 was applied or whether it was just luck.

haruspex said:
Yes, I is momentum.
Here are two methods, both valid. In both cases, I will take the positive direction as batter to pitcher:
1.
Initial momentum of ball = m(-40m/s)=-40m m/s.
Final momentum of ball = m(50m/s) = 50m m/s.
Change = 50m-(-40m) = 90m.

2.
Momentum needed to stop ball = 40m
Momentum needed to return stationary ball = 50m
Total needed = 90m.

Since master_333 was surprised his method worked, it is unclear whether method 2 was applied or whether it was just luck.

I don't understand why you did the change in momentum to get the correct answer.

master_333 said:
I don't understand why you did the change in momentum to get the correct answer.
The impulse is what changed the momentum. Impulse = change in momentum. What else would you do?

## 1. What is momentum in physics?

Momentum is a fundamental concept in physics that describes the quantity of motion an object has. It is calculated by multiplying an object's mass by its velocity.

## 2. How is momentum different from velocity?

Velocity is a measure of an object's speed and direction, while momentum also takes into account the mass of the object. Two objects with the same velocity can have different momenta if they have different masses.

## 3. How is momentum conserved in a closed system?

In a closed system, the total momentum remains constant. This means that if two objects collide, their total momentum before the collision is equal to their total momentum after the collision.

## 4. How can momentum be transferred between objects?

Momentum can be transferred between objects through collisions or interactions. In a collision, one object's momentum decreases while the other's increases. In an interaction, such as pushing or pulling, the momentum of one object is transferred to the other.

## 5. How is momentum related to force?

Force is the rate of change of an object's momentum. In other words, if a force is applied to an object, its momentum will change over time. The greater the force, the faster the object's momentum will change.

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