Net displacement for a point on a circular saw

In summary, a carpenter's circular saw with a 10.0-inch diameter blade decelerates from 4440 rpm to zero in 2.5 seconds. The angular acceleration of the blade is -29.6 rev/sec2 and the distance traveled by a point on the rim during deceleration is 242.16 feet. However, the net displacement of a point on the rim is only 10 inches, not 15.7 inches, as the displacement is determined by the straight-line distance between two points, not the distance around the circumference.
  • #1
BHFCBabe
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Homework Statement



When a carpenter shuts off his circular saw, the 10.0-inch diameter blade slows from 4440 rpm to zero in 2.5 s.
A.What is the angular acceleration of the blade? In rev/sec2
B.What is the distance traveled by a point on the rim of the blade during the deceleration? In feet.
What is the magnitude of the net displacement of a point on the rim of the blade during the deceleration? in inches

I have solved A and B, but cannot get C. The answers are in the back of the book so I know A and B are correct.

Homework Equations


1) [tex]\omega[/tex]f=[tex]\omega[/tex]o+2[tex]\alpha[/tex]t
2) [tex]\omega[/tex]f2=[tex]\omega[/tex]o2+2[tex]\alpha\Delta\Theta[/tex]

The Attempt at a Solution


A. 4440rev/1min * 1min/60sec=74 rev/sec
Using equation 1:
0=74+[tex]\alpha[/tex]*2.5
[tex]\alpha[/tex]=-29.6 rev/sec2

B. Using equation 2:
0=742+2*-29.4*[tex]\Delta\Theta[/tex]
[tex]\Delta\Theta[/tex]=92.5 Rev

1ft/12in*10pi in./1 rev * 92.5rev = 242.16 feet.

C. I know that it completed 92.5 revolutions. There are .5 revolutions left over.
10pi in/ 1 rev *.5 rev = 15.7 inches.

However, this answer is wrong. Why? The proper answer is 10 inches.
 
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  • #2
Displacement is determined by the straight-line distance between two points, not the distance around the circumference.

p.s since nobody said it to you before: welcome to Physics Forums :smile:
 
  • #3


The proper answer of 10 inches is most likely due to rounding errors. The equations used to solve for the angular acceleration and distance traveled involve decimal numbers, which can introduce rounding errors. It is possible that your calculations were slightly off, resulting in a different answer. To avoid this, it is important to use the exact values instead of rounded values when solving equations. Additionally, double check your calculations and make sure that you are using the correct units.
 

FAQ: Net displacement for a point on a circular saw

1. What is net displacement for a point on a circular saw?

Net displacement for a point on a circular saw refers to the overall distance and direction traveled by a specific point on the saw's blade in relation to its starting point.

2. How is net displacement calculated for a point on a circular saw?

The net displacement for a point on a circular saw can be calculated by finding the difference between the final and initial positions of the point. This can be done using trigonometric functions and the radius of the circular saw.

3. What factors can affect the net displacement of a point on a circular saw?

The net displacement of a point on a circular saw can be affected by the speed of rotation, the size of the circular saw, and any external forces acting on the saw, such as friction or resistance.

4. Why is net displacement important in understanding circular saw movement?

Net displacement is important in understanding circular saw movement because it helps determine the distance traveled and the direction of travel for a specific point on the blade. This information is crucial for accurately measuring and controlling the movement of the saw.

5. How can net displacement be used in the design and improvement of circular saws?

Net displacement can be used in the design and improvement of circular saws by providing insight into the efficiency and effectiveness of the saw's movement. It can also help identify areas for improvement and optimization in the saw's design and operation.

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