Simple Harmonic Motion Question Advise required please

[tomgbrown]

Simple Harmonic Motion Question... Advise required please!

A vehicle engine has a stroke of 180mm. The motion of the piston is simple harmonic.
calculate max linear velocity and acceleration at 4200rpm?
Calculate max force to the crankshaft if the piston has an effictive mass of .35kg at an amplitude of half the stroke?

I have changed 4200rpm into rad/s and multiplied that value by half of 180mm=90mm=0.09m for max linear velocity? CORRECT?/

For acceleration i have used rad/s value squared multiplied by 0.09 and it gives a huge value of 1749.7m per second per second which seems wrong to me?


For the force part of the question is it as easy as force = .35 x the acceleration value ( if its right)


Any help would be much appreciated... i think I am on the right track but need a nudge in the right direction.

Cheers, Tom Brown

 

[AlephZero]

Your method looks OK, but I think your 1749m/s^2 was a typo for an even bigger number.

That sort of acceleration is quite normal for rotating machinery. For example the centripetal acceleration of some of the rotor blades in jet engines are of the order of 100,000 m/s^2.