# When jumping straight down, you can be seriously injured if you land stiff-legged. One way to...

## Question:

When jumping straight down, you can be seriously injured if you land stiff-legged. One way to avoid injury is to bend your knees upon landing to reduce the force of the impact. Suppose you have mass {eq}m {/eq} and you jump off a wall of a height {eq}h {/eq}.

a. With what speed {eq}v {/eq}, will you hit the ground? Assume you simply step off the wall so your initial y-velocity is zero. Ignore air resistance. (Express your answer in terms of the symbols given and g for the acceleration of gravity.)

b. Suppose that the time interval starting when your feet first touch the ground until you stop is {eq}\Delta t {/eq}. Calculate the (average) net force acting on you during that interval. (Express your answer in terms of the symbols given).

c. Suppose {eq}h=1 {/eq} m. If you land stiff-legged, the time it takes you to stop may be as short as 2 ms, while if you bend your knees, it might be as long as 0.1 s. Calculate the average net force that would hit on you in the two cases.

1. What is your mass?

2. What is the average net force if you land stiff-legged?

3. What is the average net force if you bend your knees?

d. The net force on you while you are stopping includes both the force of gravity and the force of the ground pushing up. Which of these do you the injury?

i. Force of ground pushing up

ii. Force of ground

e. For the two cases in part(c), calculate the upward force the ground exerts on you.

1. What is the upward force the ground exerts on you if you land stiff-legged?

2. What is the upward force the ground exerts on you if you bend your knees?

## Force experienced in free fall and it's component:

When any particle gets free fall from some height towards Earth, the due to the gravitational force, Earth attracts that particle towards its centre. Which is known as the weight of that particle. We can resolve that force in X and Y direction and after getting component in X and Y direction, with the help of free body diagram, we can calculate forces easily.

## Answer and Explanation:

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Given data

• Mass of person = {eq}m {/eq} {eq}Kg {/eq}
• depth of wall = {eq}h {/eq} {eq}meter {/eq}

Part(a)

According to the energy conservation...

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#### Learn more about this topic: Gravitational Pull of the Earth: Definition & Overview

from

Chapter 15 / Lesson 17
29K

Earth's gravitational pull is often misunderstood, but without it, life on Earth would be impossible. In this lesson, we'll define the gravitational pull and give some examples of how it is used. A quiz is provided to test your understanding.