Posted by Jc on Sunday, October 23, 2011 at 8:32pm.
A lawn mower has a flat, rodshaped steel blade that rotates about its center. The mass of the blade is 0.65kg and its length is 0.55m. What is the rotational energy of the blade at its operating angular speed of 3450 rpm? If all of the rotational kinetic energy of the blade could be converted to gravitational potential energy, to what height would the blade rise?

Physics  Kayrie, Wednesday, March 13, 2013 at 8:13pm
Use the rotational energy equation, E = 0.5Iω², where I is the moment of inertia for a long thin rod with an axis through it's midpoint (I = (1/12)mL²).
E = 0.5Iω²
E = 0.5 [1/12)mL²] ω²
E = (1/24) mL² ω²
Find ω by multiplying the rpm by 2π and then dividing by 60 to put units into rad/sec (or multiply ω by π/30)
3450 * 2π = 21 676.9... rad/min
(21 676.9... rad/min)/60 = 361.28... rad/sec
Insert into energy eqn and solve
E = (1/24) mL² (361.28...rad/s)²
E = (1/24)(0.65kg)(0.55m²)(361.28...rad/s)²
E = ~1069 J
Answer This Question
Related Questions
 physics  An 83.2kg propeller blade measures 2.24m end to end. Model the blade ...
 physics  An 83.2kg propeller blade measures 2.24m end to end. Model the blade ...
 Physics  An 83.2kg propeller blade measures 2.24m end to end. Model the blade ...
 Physics  Consider a 52cmlong lawn mower blade rotating about its center at ...
 Physics  Consider a 59cmlong lawn mower blade rotating about its center at ...
 physics  a certain type of propeller blade can be modeled as a thin uniform bar...
 physics  An electric saw uses a circular spinning blade to slice through wood. ...
 Physics  13. The graph at right shows the angular velocity as a function of ...
 Physics  A helicopter propeller blade starts from rest and experiences a ...
 Physics  A certain type of propeller blan can be modeled as a thin uniform bar ...
More Related Questions