Calculating the Force of Impact when Stepping off a Wall

Summary

In this engaging physics tutorial, Mr. P calculates the force of impact on his body after stepping off a wall and colliding with the ground. The video breaks the problem into two parts: free fall and collision. Using concepts like momentum, Newton's second law, and conservation of mechanical energy, the solution demonstrates how to find the final velocity before impact and the force exerted during the collision. The force of impact is calculated to be approximately 220 pounds, offering a clear, practical example of physics in action.

Takeaways

• 😀 The problem involves calculating the force of impact when stepping off a wall and colliding with the ground.
• 😀 The individual's mass is 73 kg, and the wall's height is 73.2 cm, which is converted to 0.732 meters.
• 😀 The free fall portion of the problem (Part 1) calculates the final velocity just before hitting the ground.
• 😀 The collision portion (Part 2) uses Newton’s second law to calculate the force of impact during the collision with the ground.
• 😀 The initial velocity for Part 1 is zero (since the person starts from rest), and the final velocity in Part 2 is zero (since the person stops after impact).
• 😀 The final velocity before impact (Part 1) is calculated using conservation of mechanical energy, resulting in 3.79 m/s.
• 😀 The force of impact is calculated using the change in momentum divided by the time of collision, which is 0.28 seconds.
• 😀 The force of impact on the body is calculated to be approximately 988.8 N or roughly 223 lbs.
• 😀 The negative sign in the force of impact indicates that the force acts upward, decelerating the body during the collision.
• 😀 The final velocity before impact from the free fall portion becomes the initial velocity for the collision portion of the problem, connecting the two parts.

Q & A

What is the first step in solving the force of impact problem?

The first step is identifying the given information, such as mass (73 kg) and height (73.2 cm, which is converted to 0.732 meters), and recognizing that the initial velocity during free fall is zero.

Why is the velocity at the end of the free fall phase equal to the initial velocity for the collision phase?

The velocity at the end of the free fall phase is equal to the initial velocity for the collision phase because these two phases are connected: the moment just before hitting the ground marks the beginning of the collision.

What principle is used to calculate the velocity at the end of the free fall phase?

The principle of conservation of mechanical energy is used. The gravitational potential energy at the start of free fall is converted to kinetic energy at the point just before hitting the ground.

What equation is used to solve for the force of impact?

The equation used is the version of Newton's second law: Net force equals change in momentum divided by change in time.

How is momentum related to mass and velocity?

Momentum is the product of mass and velocity. It is a vector quantity, meaning it has both magnitude and direction.

Why is it necessary to split the problem into two parts?

The problem is split into two parts—free fall and collision—because different principles and equations apply to each phase. Free fall uses conservation of energy, while the collision uses Newton’s second law.

What does the negative sign in the velocity represent?

The negative sign indicates that the velocity is directed downward. It represents the direction of motion during free fall.

Why is it important to correctly interpret the direction of the force of impact?

It is important because the force of impact must act upwards to slow down the body. If the direction were incorrectly calculated as down, it would suggest that the body is being pushed downward instead of being stopped.

What is the force of impact calculated to be in Newtons, and what does this represent?

The force of impact is calculated to be approximately 990 Newtons. This is the net upward force acting on the body to slow it down during the collision.

How does the force of impact relate to everyday experiences or practical scenarios?

The force of impact is similar to what you might feel when landing from a jump or falling. The result, about 220 pounds of force, helps to visualize how much force is needed to stop a body quickly during a fall.