# Calculating Kinetic Energy and Average Force in a Wall Push Experiment

• Tubs
In summary, the conversation discusses a physics problem involving a person pushing against a wall to stop themselves. The questions focus on finding the change in kinetic energy, average force exerted on the wall, initial and final velocities, distance covered, and the formula for force. The solution involves using the Work-Energy theorem or kinematics to calculate the average force. The center of mass is not necessary for solving this problem.
Tubs
I don't understand how to approach this question, I'm lost in where energy gets involved. Any help would be appreciated

A 110kg person is traveling at 3 m/s on a frictionless surface toward a wall, then stops themselves by pushing against the wall. During the push, the person's center of mass moves 0.3 m toward the wall. What is the change of the person's kinetic energy, and what is the average force exerted on the wall?

answer these questions and see how you can connect them to each other
what is the
initial velocity?
final velocity?
Given the above two can you find the change in kinetic energy?

Also what is the distance covered while stopping?
What is the formula for force?
Givne the first three quantities, V2, V1 and D, can you find the force? Hint: what is the formula for force? What you need in that formula.

So the change in kinetic energy would be

Kf - Ki = chng in K

where Kf = 0 and Ki = 1/2 (110kg)(3m/s) = 165J

chng in K = 165 J

and for the second part I'm still confused on what formula to use, would the distance covered during the stop be x2 in:

Xcom = [m(x1) + m(x2)] / m ?

I don't think it is

KE = (1/2)mv²

Yeah, I caught that error. How to get the average force still boggles me though

This problem has nothing to do with calculating the center of mass. It's an application of the "Work-Energy theorem". (Look it up.)

If you haven't covered that theorem, you can always find the average acceleration (using kinematics) and apply Newton's 2nd law to get the average force.

So center of mass isn't needed at all? I just assumed it would be because the question came out of the center of mass chapter in my textbook.

All you need to know is the displacement of the center of mass...and that's given.

## What is the definition of center of mass?

The center of mass is a point in an object or system where the mass is evenly distributed in all directions. It is the point at which an object will balance and rotate around if suspended.

## How is center of mass calculated?

The center of mass is calculated by finding the average position of all the mass in an object. This is done by dividing the sum of all the mass multiplied by their respective positions by the total mass of the object.

## Why is center of mass important?

The center of mass is important because it helps determine the stability and balance of an object. It also plays a crucial role in understanding the motion and dynamics of objects, particularly in physics and engineering.

## Can the center of mass be outside of an object?

Yes, the center of mass can be outside of an object, especially in irregularly shaped objects or objects with non-uniform density. In these cases, the center of mass may not correspond to an actual physical point in the object.

## How does the center of mass change with different body positions?

The center of mass changes with different body positions because the distribution of mass within the body changes. For example, when a person stands on one leg, their center of mass shifts towards the supporting leg. This can affect their balance and stability.

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