Physics question about momentum

In summary, the average vector force the ball exerts on the bat during their interaction is negative.
  • #1
bona0002
15
0
Hey guys,

I'm currently taking the first physics course right now (calculus-based physics), but it's not going as smoothly as I would've hoped. Anyways, here's one of the many questions I shall be posing on the forum: A baseball approaches home plate at a speed of 47.0 m/s, moving horizontally just before being hit by a bat. The batter hits a pop-up such that after hitting the bat, the baseball is moving at 50.0 m/s straight up. The ball has a mass of 145 g and is in contact with the bat for 1.80 ms. What is the average vector force the ball exerts on the bat during their interaction?

Now, I know how to draw the diagram to visualize the approach, I know that ρ = m * v, and I know that force = Δp/Δt. When I get my final answer, the components of the average force are (-3786i + 4028j)N. However, the answer has the signs reversed. Why is that the case?

Thanks in advance for the help!
 
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  • #2
bona0002 said:
Hey guys,

I'm currently taking the first physics course right now (calculus-based physics), but it's not going as smoothly as I would've hoped. Anyways, here's one of the many questions I shall be posing on the forum: A baseball approaches home plate at a speed of 47.0 m/s, moving horizontally just before being hit by a bat. The batter hits a pop-up such that after hitting the bat, the baseball is moving at 50.0 m/s straight up. The ball has a mass of 145 g and is in contact with the bat for 1.80 ms. What is the average vector force the ball exerts on the bat during their interaction?

Now, I know how to draw the diagram to visualize the approach, I know that ρ = m * v, and I know that force = Δp/Δt. When I get my final answer, the components of the average force are (-3786i + 4028j)N. However, the answer has the signs reversed. Why is that the case?

Thanks in advance for the help!

Hi bona0002, Welcome to Physics Forums.

The signs will depend upon your choice of coordinate axes. Be sure to apply them consistently for all vector quantities (velocities, momenta).
 
  • #3
bona0002 said:
Hey guys,

I'm currently taking the first physics course right now (calculus-based physics), but it's not going as smoothly as I would've hoped. Anyways, here's one of the many questions I shall be posing on the forum: A baseball approaches home plate at a speed of 47.0 m/s, moving horizontally just before being hit by a bat. The batter hits a pop-up such that after hitting the bat, the baseball is moving at 50.0 m/s straight up. The ball has a mass of 145 g and is in contact with the bat for 1.80 ms. What is the average vector force the ball exerts on the bat during their interaction?

Now, I know how to draw the diagram to visualize the approach, I know that ρ = m * v, and I know that force = Δp/Δt. When I get my final answer, the components of the average force are (-3786i + 4028j)N. However, the answer has the signs reversed. Why is that the case?

Thanks in advance for the help!

If the i direction represents direction from home plate to center field then the i component of force should be +. But then the y-axis must point dow, a strange choice in my opinion but entirely permissible.
 
  • #4
That makes sense. Thanks guys!
 
  • #5


I would first commend you for seeking out help and actively engaging in problem-solving for your physics course. It is important to ask questions and seek clarification when something is not clear, and it shows your dedication to understanding the material.

Now, to address your specific question about the signs being reversed in your final answer, it is important to remember that momentum is a vector quantity and has both magnitude and direction. In this case, the direction of the momentum change for the baseball is in the negative x-direction (i.e. the opposite direction of its initial velocity) and in the positive y-direction (as it is moving up after being hit by the bat). This means that the change in momentum is negative in the x-direction and positive in the y-direction, resulting in the negative and positive signs in your final answer.

I would also like to point out that your approach and use of equations is correct, and it is great that you are able to visualize the situation and draw a diagram to aid in your understanding. Keep up the good work and don't be discouraged by challenges in your physics course. With practice and determination, you will continue to improve and excel in your studies. Good luck!
 

What is momentum?

Momentum is a physical quantity that describes the motion of an object. It is defined as the product of an object's mass and its velocity, and is a vector quantity, meaning it has both magnitude and direction.

How is momentum calculated?

Momentum is calculated by multiplying an object's mass (m) by its velocity (v): p = m * v. The standard unit of momentum is kilogram-meters per second (kg*m/s).

What is the principle of conservation of momentum?

The principle of conservation of momentum states that in a closed system, the total momentum before a collision or interaction is equal to the total momentum after the collision or interaction. This means that momentum is conserved, or stays the same, in a closed system.

What is the difference between linear and angular momentum?

Linear momentum refers to the momentum of an object moving in a straight line, while angular momentum refers to the momentum of an object rotating around an axis. Both types of momentum are conserved in a closed system.

What are some real-life applications of momentum?

Momentum is a fundamental concept in many areas of physics and has many real-life applications. Some examples include the study of collisions in sports, the behavior of objects in space, and the design of efficient transportation systems.

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