Exercise 8.5 Hints: Getting Started | I'm Stuck Suppose a 427 kg alligator of length 3.4 m is stretched out on a board of the same length weighing 95 N. If the board is supported on the ends as in Figure 8.10, and the scale reads 1967 N, find the x-component of the alligator's center of gravity. X m Xcg, alligator = How many forces are exerted on the board? What is the torque exerted by each one? Since the board is at rest, the net torque must be zero.

College Physics
11th Edition
ISBN:9781305952300
Author:Raymond A. Serway, Chris Vuille
Publisher:Raymond A. Serway, Chris Vuille
Chapter1: Units, Trigonometry. And Vectors
Section: Chapter Questions
Problem 1CQ: Estimate the order of magnitude of the length, in meters, of each of the following; (a) a mouse, (b)...
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**Exercise 8.5**

Suppose a 427 kg alligator of length 3.4 m is stretched out on a board of the same length weighing 95 N. If the board is supported on the ends as in Figure 8.10, and the scale reads 1967 N, find the x-component of the alligator's center of gravity.

\[ x_{cg, \text{alligator}} = \] ☐ m

How many forces are exerted on the board? What is the torque exerted by each one? Since the board is at rest, the net torque must be zero.

**Hints: Getting Started | I'm Stuck**

---

### Explanation for Educational Website:

This problem involves calculating the center of gravity of an alligator placed on a board. The alligator weighs 427 kg and has a length of 3.4 meters. The board it lies on is of the same length and weighs 95 N. The board is supported at both ends. To solve this problem, you will need to use the principles of equilibrium and torque, where the system should balance with a net torque of zero to remain at rest.

To find the x-component of the alligator's center of gravity (\(x_{cg, \text{alligator}}\)), consider all forces acting on the board and the torques they exert around a chosen pivot point. Use the reading from the scale (1967 N) as a force exerted on the board and establish equations that satisfy equilibrium conditions for both forces and torques.

By applying these principles, you'll better understand how forces and torque interact to maintain balance in static systems.
Transcribed Image Text:**Exercise 8.5** Suppose a 427 kg alligator of length 3.4 m is stretched out on a board of the same length weighing 95 N. If the board is supported on the ends as in Figure 8.10, and the scale reads 1967 N, find the x-component of the alligator's center of gravity. \[ x_{cg, \text{alligator}} = \] ☐ m How many forces are exerted on the board? What is the torque exerted by each one? Since the board is at rest, the net torque must be zero. **Hints: Getting Started | I'm Stuck** --- ### Explanation for Educational Website: This problem involves calculating the center of gravity of an alligator placed on a board. The alligator weighs 427 kg and has a length of 3.4 meters. The board it lies on is of the same length and weighs 95 N. The board is supported at both ends. To solve this problem, you will need to use the principles of equilibrium and torque, where the system should balance with a net torque of zero to remain at rest. To find the x-component of the alligator's center of gravity (\(x_{cg, \text{alligator}}\)), consider all forces acting on the board and the torques they exert around a chosen pivot point. Use the reading from the scale (1967 N) as a force exerted on the board and establish equations that satisfy equilibrium conditions for both forces and torques. By applying these principles, you'll better understand how forces and torque interact to maintain balance in static systems.
## Example 8.5 Locating Your Lab Partner's Center of Gravity

### Goal
Use torque to find a center of gravity.

### Problem
In this example, we show how to find the location of a person's center of gravity. Suppose your lab partner has a height \( L \) of 176 cm (5 ft, 9 in) and a weight \( w \) of 696 N (156 lb). You can determine the position of his center of gravity by having him stretch out on a uniform board supported at one end by a scale, as shown in Figure 8.10.

*If the board's weight \( w_b \) is 44 N and the scale reading \( F \) is \( 3.06 \times 10^2 \) N, find the distance of your lab partner's center of gravity from the left end of the board.*

### Strategy
To find the position \( x_{cg} \) of the center of gravity, compute the torques using an axis through \( O \). Set the sum of the torques equal to zero and solve for \( x_{cg} \).

### Solution
Apply the second condition of equilibrium. There is no torque due to the normal force \( \vec{n} \) because its moment arm is zero.

Solve for \( x_{cg} \) and substitute known values.

\[
\Sigma \tau_0 = 0
\]

\[
-wx_{cg} - w_b(L/2) + FL = 0
\]

\[
x_{cg} = \frac{FL - w_b(L/2)}{w}
\]

\[
x_{cg} = \frac{(306.24 \, \text{N})(176 \, \text{cm}) - (44 \, \text{N})(88 \, \text{cm})}{696 \, \text{N}}
\]

\[
x_{cg} = 72 \, \text{cm}
\]

### Remarks
The given information is sufficient only to determine the \( x \) coordinate of the center of gravity. The other two coordinates can be estimated, based on the body's symmetry.

### Figure Description
The diagram shows a person lying on a uniform board. The board is supported at one end by a scale. The diagram indicates the placement of forces \( F \) on the scale, \( \vec{n}
Transcribed Image Text:## Example 8.5 Locating Your Lab Partner's Center of Gravity ### Goal Use torque to find a center of gravity. ### Problem In this example, we show how to find the location of a person's center of gravity. Suppose your lab partner has a height \( L \) of 176 cm (5 ft, 9 in) and a weight \( w \) of 696 N (156 lb). You can determine the position of his center of gravity by having him stretch out on a uniform board supported at one end by a scale, as shown in Figure 8.10. *If the board's weight \( w_b \) is 44 N and the scale reading \( F \) is \( 3.06 \times 10^2 \) N, find the distance of your lab partner's center of gravity from the left end of the board.* ### Strategy To find the position \( x_{cg} \) of the center of gravity, compute the torques using an axis through \( O \). Set the sum of the torques equal to zero and solve for \( x_{cg} \). ### Solution Apply the second condition of equilibrium. There is no torque due to the normal force \( \vec{n} \) because its moment arm is zero. Solve for \( x_{cg} \) and substitute known values. \[ \Sigma \tau_0 = 0 \] \[ -wx_{cg} - w_b(L/2) + FL = 0 \] \[ x_{cg} = \frac{FL - w_b(L/2)}{w} \] \[ x_{cg} = \frac{(306.24 \, \text{N})(176 \, \text{cm}) - (44 \, \text{N})(88 \, \text{cm})}{696 \, \text{N}} \] \[ x_{cg} = 72 \, \text{cm} \] ### Remarks The given information is sufficient only to determine the \( x \) coordinate of the center of gravity. The other two coordinates can be estimated, based on the body's symmetry. ### Figure Description The diagram shows a person lying on a uniform board. The board is supported at one end by a scale. The diagram indicates the placement of forces \( F \) on the scale, \( \vec{n}
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