High School

In order for a lawn mower blade to cut grass, it must strike the grass with a speed of at least 900 in/s. If the innermost part of the cutting edge is 6 in from the center of the blade, how many radians per second must the blade turn? How many revolutions per minute is this?

Answer :

The lawn mower blade must turn at 1800 radians per second. The blade must turn at approximately 286.48 revolutions per minute to achieve a linear cutting edge speed of at least 900 in/s.

To determine how many radians per second the lawn mower blade must turn and how many revolutions per minute (rpm) this corresponds to, you can use the following information:

The linear speed of the blade's cutting edge should be at least 900 in/s.

The innermost part of the cutting edge is 6 inches from the center of the blade.

First, calculate the angular speed (in radians per second):

Angular Speed (ω) = Linear Speed (v) / Radius (r)

Where:

Linear Speed (v) = 900 in/s

Radius (r) = 6 inches

Convert the radius to feet (1 foot = 12 inches):

r = 6 inches / 12 = 0.5 feet

Now, calculate ω:

ω = 900 in/s / 0.5 feet = 1800 rad/s

So, the lawn mower blade must turn at 1800 radians per second.

To find the number of revolutions per minute (rpm), you can use the conversion:

1 revolution = 2π radians

ω (in rpm) = (ω (in rad/s)) / (2π)

ω (in rpm) = 1800 rad/s / (2π) ≈ 286.48 rpm

So, the blade must turn at approximately 286.48 revolutions per minute to achieve a linear cutting edge speed of at least 900 in/s.

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