# High School Physics Question -- Skateboarder Jumps & Conservation of Momentum

• Kate2018
In summary, Lee riding on her 6 kg skateboard with a constant speed of 2 m/s jumps off and continues forward with a velocity of 4 m/s relative to the ground, causing the skateboard to go flying forward with a speed of 18.5 m/s relative to the ground. The question asks for Lee's mass, but there are missing details and assumptions that make this a poorly constructed problem.
Kate2018

## Homework Statement

Lee is riding on her 6 kg skateboard with a constant speed of 2 m/s. She jumps off of her skateboard and continues forward with a velocity of 4 m/s relative to the ground. This causes the skateboard to go flying forward with a speed of 18.5 m/s relative to the ground. What is Lee’s mass?

## Homework Equations

m1v1+m2v2= (m1+m2)v3
m1v1+m2v2=m1v3+m2v4

Info
m1=?
v1= 2m/s
m2= 6kg
v2=2m/s
v3=4m/s
v4= 18.5m/s

Kate2018 said:

## Homework Statement

Lee is riding on her 6 kg skateboard with a constant speed of 2 m/s. She jumps off of her skateboard and continues forward with a velocity of 4 m/s relative to the ground. This causes the skateboard to go flying forward with a speed of 18.5 m/s relative to the ground. What is Lee’s mass?

## Homework Equations

m1v1+m2v2= (m1+m2)v3
m1v1+m2v2=m1v3+m2v4

## The Attempt at a Solution

Info
m1=?
v1= 2m/s
m2= 6kg
v2=2m/s
v3=4m/s
v4= 18.5m/s
So the skateboarder jumps off faster forward and the skateboard goes forward faster too. That would be a great way to create free energy... I guess I'm missing something...

Abhishek kumar
berkeman said:
So the skateboarder jumps off faster forward and the skateboard goes forward faster too. That would be a great way to create free energy... I guess I'm missing something...
Kate2018 said:

## Homework Statement

Lee is riding on her 6 kg skateboard with a constant speed of 2 m/s. She jumps off of her skateboard and continues forward with a velocity of 4 m/s relative to the ground. This causes the skateboard to go flying forward with a speed of 18.5 m/s relative to the ground. What is Lee’s mass?

## Homework Equations

m1v1+m2v2= (m1+m2)v3
m1v1+m2v2=m1v3+m2v4

## The Attempt at a Solution

Info
m1=?
v1= 2m/s
m2= 6kg
v2=2m/s
v3=4m/s
v4= 18.5m/s
Go and check your problem details again something is missing i guess.

Kate2018 said:

## Homework Statement

Lee is riding on her 6 kg skateboard with a constant speed of 2 m/s. She jumps off of her skateboard and continues forward with a velocity of 4 m/s relative to the ground. This causes the skateboard to go flying forward with a speed of 18.5 m/s relative to the ground. What is Lee’s mass?

## Homework Equations

m1v1+m2v2= (m1+m2)v3
m1v1+m2v2=m1v3+m2v4

## The Attempt at a Solution

Info
m1=?
v1= 2m/s
m2= 6kg
v2=2m/s
v3=4m/s
v4= 18.5m/s

I suspect the skateboard is supposed to go flying backwards.

That said, this is a poor question. You have to assume that there is no friction possible between the skateboard and the ground. In general, when you jump the Earth is involved. So, it's not good to develop the idea that conservation of momentum applies to jumping.

berkeman

## 1. What is the law of conservation of momentum?

The law of conservation of momentum states that in a closed system, the total momentum before an event must be equal to the total momentum after the event. This means that momentum cannot be created or destroyed, only transferred from one object to another.

## 2. How does the conservation of momentum apply to a skateboarder jumping?

When a skateboarder jumps, the skateboard and the skateboarder are considered a closed system. The initial momentum of the system before the jump is equal to the final momentum of the system after the jump. This means that the skateboarder will have the same momentum as the skateboard, but in the opposite direction.

## 3. What factors affect the momentum of a skateboarder during a jump?

The momentum of a skateboarder during a jump is affected by their mass, velocity, and the height and distance of the jump. The greater the mass and velocity of the skateboarder, the greater their momentum will be. Additionally, the higher and farther the skateboarder jumps, the greater their momentum will be.

## 4. How does the principle of conservation of energy relate to the conservation of momentum?

The principle of conservation of energy states that energy cannot be created or destroyed, only transferred from one form to another. This is closely related to the conservation of momentum, as momentum is a form of energy. In a closed system, the total energy before an event must be equal to the total energy after the event.

## 5. Why is the conservation of momentum important in physics?

The conservation of momentum is important in physics because it is a fundamental law that helps us understand and predict the behavior of objects in motion. It is used to analyze a wide range of physical phenomena, from collisions to rocket propulsion. It also allows us to make calculations and predictions based on known quantities, making it an essential concept in many fields of science and engineering.

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