Understanding Momentum and Impulse

In summary, a hockey player exerts a force of 30.0N on a hockey puck for 0.16 seconds, resulting in an impulse of 4.8. The puck, with a mass of 0.115 kg and at rest before the shot, heads towards the goal with an unknown speed. Using the equation p=mv, the change in momentum can be calculated, which is equal to the impulse. By using the formula FΔt=Δ(mv), the final velocity of the puck can be found by solving for v, and then the momentum can be calculated with the final velocity. The change in momentum, or impulse, is equal to the change
  • #1
Sonny18n
60
0

Homework Statement


1) A hockey player makes a slap shot, exerting a force of 30.0N on the hockey pock for 0.16 seconds. What impulse is given to the puck?

2) The hockey puck shot in exercise 1 has a mass of 0.115 kh and was at rest before the shot. With what speed does it head toward the goal.

Homework Equations


p=mv

(F)triangle(t)= Triangle(p)

The Attempt at a Solution


1. If I'm using impulse formula correctly than multiplying 30N and 0.16 sec is 4.8

2) I have a harder time understanding this, I'm not even sure if it's asking me to use the formula for momentum[/B]
 
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  • #2
Sonny18n said:
1. If I'm using impulse formula correctly than multiplying 30N and 0.16 sec is 4.8
Units?

Sonny18n said:
2) I have a harder time understanding this, I'm not even sure if it's asking me to use the formula for momentum
What is the relation between momentum and speed?
 
  • #3
The solution can be found starting with with Newtons classic:
f = m * a
Think about the definition for acceleration (a).
 
  • #4
dean barry said:
The solution can be found starting with with Newtons classic:
f = m * a
Think about the definition for acceleration (a).
Yes, but given the first part of the question I would think the intent is to use momentum.
 
  • #5
Ok so how do I find the acceleration
 
  • #6
Sonny18n said:
Ok so how do I find the acceleration
You don't need to. See DrClaude's post.
 
  • #7
haruspex said:
You don't need to. See DrClaude's post.
That's all the question says, the "at rest" part is kind of throwing me off
 
  • #8
Sonny18n said:
That's all the question says, the "at rest" part is kind of throwing me off
Why? Suppose it moves off at speed v. How much is the increase in speed? What is the increase in momentum?
 
  • #9
Force * time gives the value for impulse.
The result equals the change in momentum, during the impulse.
The original momentum is 0
 
  • #10
dean barry said:
Force * time gives the value for impulse.
The result equals the change in momentum, during the impulse.
Sonny18n already did that bit in part 1. DrClaude and I are trying to get Sonny18n to use that result together with the puck mass to solve part 2 directly rather than going back to the force given. I (we?) feel this is the intent of the question, and clearly something Sonny18n needs to learn how to do. The force * time approach is not always available, because it only works when the force is constant. Yes, it's constant here, but in other momentum questions it won't be.
 
  • #11
haruspex said:
Why? Suppose it moves off at speed v. How much is the increase in speed? What is the increase in momentum?
At rest means 0m/s right? So it won't affect the equation in a major way. But it's asking me to relate the answer from question 1 but it's not clear to me how impulse I can find the speed it takes.
 
  • #12
Sonny18n said:
At rest means 0m/s right? So it won't affect the equation in a major way. But it's asking me to relate the answer from question 1 but it's not clear to me how impulse I can find the speed it takes.
Impulse is momentum. How do you normally assess the momentum of an object?
 
  • #13
Sonny18n said:
At rest means 0m/s right? So it won't affect the equation in a major way. But it's asking me to relate the answer from question 1 but it's not clear to me how impulse I can find the speed it takes.
haruspex said:
Impulse is momentum. How do you normally assess the momentum of an object?
Mass times velocity?
 
  • #14
Sonny18n said:
Mass times velocity?
Yes.
 
  • #15
haruspex said:
Yes.
So the velocity is 0m/s then or..?
 
  • #16
Sonny18n said:
So the velocity is 0m/s then or..?
If the momentum is mass times velocity, what do you think a change in momentum for an object equals?
 
  • #17
haruspex said:
If the momentum is mass times velocity, what do you think a change in momentum for an object equals?
But I don't have momentum. Only mass and no velocity
 
  • #18
Sonny18n said:
But I don't have momentum. Only mass and no velocity
You have change in momentum and mass, and you want change in velocity.
 
  • #19
the first question is asking about impusle which the formula is ft=mv-mu. So in order to get the impulse just multiply the force given and the time. You may ask where does ft=mv-mu came from, it is derived from the F=ma. Acceleration equals to v-u/t. So when yiu substitute v-u/t into the acceleration , you will get F=mv-mu/t. The t is taken to the left side of the equation and it becomes Ft=mv-mu. mv-mu is the impulse and so ft is also impulse
 
  • #20
Keep in mind that momentum is conserved, meaning that it can not change unless there is an outside influence acting on it- an impulse.

 
  • #21
Your two equations tell the whole story. If you combine them, you get:
$$FΔt=Δ(mv)$$
What is F and Δt in your problem?
What is mv to begin with?
You are trying to find the final value of v from this equation. You do know how to express Δ(mv) algebraically in terms of the initial and final velocities of the puck, correct?

Chet
 
  • #22
You could go by another route, use Newtons classic relationship: f = m * a
( transpose for acceleration a )
Then find the velocity after time t
Calculate the momentum.
( m * v )
 

What is momentum?

Momentum is a property of a moving object that describes its tendency to keep moving in the same direction and at the same speed.

What is impulse?

Impulse is a change in momentum that occurs when a force is applied to an object for a certain amount of time.

How are momentum and impulse related?

Momentum and impulse are directly related. The greater the impulse applied to an object, the greater the change in its momentum.

Why is understanding momentum and impulse important?

Understanding momentum and impulse is important in many areas of physics, including mechanics, collisions, and motion. It allows us to understand and predict the behavior of objects in motion.

What are some real-world applications of momentum and impulse?

Momentum and impulse are important in sports, such as football and baseball, to understand the motion of players and objects. They are also crucial in transportation, as they help engineers design safer cars and trains.

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