Posted by **Camilla** on Saturday, June 16, 2012 at 10:33am.

Consider a 59-cm-long lawn mower blade rotating about its center at 2990 rpm.

(a) Calculate the linear speed of the tip of the blade.

(b) If safety regulations require that the blade be stoppable within 3.0 s, what minimum angular acceleration will accomplish this? Assume that the angular acceleration is constant.

The answers are a) 92.4 m/s and b) -104 rad/s^2. How do I get these answers? Thank you in advance.

- Physics -
**ajayb**, Saturday, June 16, 2012 at 12:19pm
a) linear speed v = w*r (where w is the angular speed in radians/sec and r is the radial distance from the center)

Here, w = 2990 rpm = 49.83 rev.per sec.

= 49.83*2*pi rad/sec

=313.11 rad/sec

& r = 0.59/2 = 0.295 m

So, v = 313.11*0.295 = 92.4m/s

b) w(final) = w(initial) + alpha*t

0 = 313.11 + alpha*3

alpha = -313.11/3 = -104rad/s^2

- Physics -
**Elena**, Saturday, June 16, 2012 at 5:03pm
n=3390 rev/min=3390/60 rev/s

D= 0.52 m R= 0.26 m.

v=ω•R =2•π•n•R= 2• π•339•0.26/6 =92.3 m/s,

ω (fin)= ω - ε•t.

ω (fin)=0,

ε = ω /t = 339/6•3 =18.8 rad/s²

## Answer this Question

## Related Questions

Physics - Consider a 52-cm-long lawn mower blade rotating about its center at ...

Physics - A lawn mower has a flat, rod-shaped steel blade that rotates about its...

physics - An 83.2-kg propeller blade measures 2.24m end to end. Model the blade ...

physics - An 83.2-kg propeller blade measures 2.24m end to end. Model the blade ...

Physics - An 83.2-kg propeller blade measures 2.24m end to end. Model the blade ...

Physics - 1. A model of a helicopter rotor has four blades, each 2.50 m in ...

physics - Rotating blade (body force in axial loading) A blade is fixed to a ...

physics - Rotating blade (body force in axial loading) blade is fixed to a ...

physics - The large blade of a helicopter is rotating in a horizontal circle. ...

physics - The large blade of a helicopter is rotating in a horizontal circle. ...