Question
question 2
An Olympic figure skater having a mass of 48 kg glides across the ice at 2.8 meters/second. What is her linear momentum? What is her kinetic energy? Then, she leaps and lands on the toe of one skate, twirling into a graceful pirouette, with her arms held tightly together straight up over her head. As an engineer, you know she has merely converted translational motion into rotational motion. If her body can be modeled as being a circular cylinder with a radius of 0.32 meters, how many rpm (revolutions per minute) is she rotating? She then fully extends her arms, straight out from her shoulders. Assume her arms can be modeled as slender bars, each 0.85 meters long and having a mass of 5 kg. What is her new rotational speed in rpm? My car engine can deliver a maximum of 112 ft-lbf of torque when running at 3200 rpm. How many horsepower is the engine producing at this same time?
Explanation / Answer
Power = torque * angular speed
torque=112 ft-lbf =151.85184 n.m
angular speed= 3200rpm =3200*(2 pi/60)=335.103 rad/s
Power=151.851n.m*335.103rad/s=50886.04 Watt
1 watt =0,00134102 hp
Power=68.239 HP
