Physics in vertical jump and basball hit

In summary, the conversation discusses various physics problems related to movies and sports. The first problem involves calculating the force of a vertical jump based on the height, time to reach the top, and mass of the person. The second problem involves determining the bat speed in a baseball scenario. The third problem addresses the distance a runner would slide on ice after falling at a certain speed. Further information and equations are needed to solve these problems accurately.
  • #1
Michael12438
3
0

Homework Statement


Okay so these are from movies. I am trying to prove them right or wrong using physics. how can I figure out the pounds of force of a vertical jump when I have the:

height of the jump = 6 feet
Time to reach top = .797 sec
Mass of person = 100lbs
2. How can I figure out this problem...

If a baseball is thrown with a velocity of 90mph, and the ball exits the bat at 140mph, what eas the bat speed? Consider the ball was hit with a wood bat. On its most dense part with the barell diameter of 2.5 in, the bat is 30 oz

Friction- how far would a runner slide if he fell on ice after running 15 mph

Homework Equations

The Attempt at a Solution


For the first one I messed up somehow using the fact that initial velocity was 0m/s^2 and I got that the force would be only around 50lbs. The number should be in te thousands I'm suspecting. Please help
 
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  • #2
Michael12438 said:
the pounds of force of a vertical jump
You have to make some assumption about how the force varies over the period before leaving the ground. Constant is a bit unrealistic as it means power increases linearly with speed. Constant power might be nearer the mark.
Michael12438 said:
height of the jump = 6 feet
Be careful how you define that. It's the movement of the mass centre that's important for the forces etc. Most vertebrates can only get their mass centres up about three feet from the point of leaving the ground.
Michael12438 said:
Time to reach top = .797 sec
From starting the jump (from crouching? How low?) or from lift off?
Michael12438 said:
If a baseball is thrown with a velocity of 90mph, and the ball exits the bat at 140mph
You will also need to know the mass of the ball; and the coefficient of restitution... or you could just suppose it to be perfectly elastic.
Michael12438 said:
On its most dense part with the barell diameter of 2.5 in
I don't see how the diameter matters. I guess you mean the bat is struck at its mass centre.
Michael12438 said:
Friction- how far would a runner slide if he fell on ice after running 15 mph
Again, you need more data. What do you think that might be?
 
  • #3
For the friction what other data do I need?

The mass of the ball is 5 oz

The height of the jump is 6 feet. It is from a movie and I'm trying to prove it is not realistic

I don't know what restitution is.
 
  • #4
The jump time is from lift off and using the mass center
 
  • #5
Michael12438 said:
For the friction what other data do I need?
You are trying to calculate a distance given an initial speed and a final speed. You don't know the time, so what else will help?
Michael12438 said:
The mass of the ball is 5 oz
What equations do you know related to collisions? What is or may be conserved?
Michael12438 said:
I don't know what restitution is.
It's a measure of how well bodies rebound from collisions. Take two bodies, initially moving at speeds u1, v1. Positive is to the right, say. Take it all to be in one straight line. After collision, they move off with speeds u2, v2. It turns out that if you were to repeat the experiment with the same bodies at different speeds you would find there is a constant (usually written as e, for elasticity, or R for restitution) such that v2-u2 = R(u1-v1). (Note the sign reversal.) For more info G**gle for coefficient of restitution.
In a perfectly elastic collision, the coefficient is 1. The fraction of energy retained is the square of the coefficient.
Michael12438 said:
The jump time is from lift off and using the mass center
Mass centre up 6 feet - definitely unrealistic.
What take-off speed would be needed? What SUVAT equations do you know? (You should have listed these in the OP.)
 

FAQ: Physics in vertical jump and basball hit

1. How does physics play a role in vertical jump?

The physics of vertical jump involves the principles of force, acceleration, and gravity. When a person jumps, they push against the ground with their feet, creating a force that propels them upwards. As they push off, their body accelerates due to the force and the opposing force of gravity. The higher the force and acceleration, the higher the vertical jump.

2. What is the relationship between force and mass in a baseball hit?

The relationship between force and mass is described by Newton's Second Law of Motion, which states that force is equal to mass multiplied by acceleration. In a baseball hit, the force of the bat hitting the ball is directly related to the mass of the bat and the acceleration of the swing. A heavier bat or a faster swing will result in a greater force and a more powerful hit.

3. How does air resistance affect a baseball hit?

Air resistance, also known as drag, can greatly impact a baseball hit. As the ball travels through the air, it experiences a force in the opposite direction of its motion due to the friction of the air molecules. This can cause the ball to slow down and drop sooner than expected. To minimize the effects of air resistance, baseball players often use techniques such as swinging the bat in a smooth and streamlined manner.

4. What is the optimal angle for a baseball bat to hit a home run?

The optimal angle for a baseball bat to hit a home run depends on various factors such as the velocity of the ball, the mass and speed of the bat, and the distance to the home run fence. However, research has shown that a bat angle of around 35 degrees is most effective in achieving a home run. This angle allows for a balance between maximizing the distance the ball travels and minimizing the effects of air resistance.

5. How does the center of mass affect a vertical jump and baseball hit?

The center of mass is the point at which an object's mass is evenly distributed. In a vertical jump, the center of mass plays a crucial role in maintaining balance and stability during takeoff and landing. In a baseball hit, the center of mass of the bat and the ball can affect the trajectory and spin of the ball. A well-balanced bat with a lower center of mass can result in a more accurate and powerful hit.

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