the_sunshine

Thank you very much! Regards!

Could anyone point out my mistake? Thanks. The range of human hearing extends from approximately 20 Hz to 20,000 Hz. Find the wavelengths of these extremes at a temperature of 40°C. 20 Hz = 1.07 m Your answer differs from the correct answer by orders of magnitude. 20,000 Hz = 0.00107 m Your answer differs from the correct answer by orders of magnitude. V=(331)*(sq.root of T)/273K T=40 C= 313K V=(331)* (sq.root of 313K)/273= 21.5m/s V=frequency*lambda Lambda=21.5/20= 1.075m Lambda=21.5/20000= 0.001075m

ok, thanks!

the answer for KE i got

yes, but it's still wrong

so is it my mistake in the formula? KE=1/2 m*v^2 i'm sorry, i still cannot understand. could you be more specific?

A car is designed to get its energy from a rotating flywheel with a radius of 1.50 m and a mass of 575 kg. Before a trip, the flywheel is attached to an electric motor, which brings the flywheel's rotational speed up to 4500 rev/min. (a) Find the kinetic energy stored in the flywheel. (b) If the flywheel is to supply energy to the car as would a 10.0-hp motor, find the length of time the car could run before the flywheel would have to be brought back up to speed. I tried: Part a) w=4500rev/min*2PR/60= 706.5m/sec I=mass*R^2=575kg*(1.50m)^2= 1293.75 kg*m^2 Then, KE=1/2*I*w^2 = 1/2 (1293.75 kg*m^2) * (706.5 m/s)^2 = 322 895 153.9 J Part b) Power = d*w/d*t And it is wrong. I cannot go to part b with incorrect answer in a. Can anyone please try to explain to me what am i doing wrong?

i got it. Thank You!

velocity = radius * angular velocity v1=3.8m*450rev/min= 1710/60 = 28.5m/s v2=0.51m*4150rev/min=2116.5/60 = 35.3m/s Comparison with the speed of sound: vmain rotor / vsound = 28.5m/s/343 m/s= 0.083 vtail rotor / vsound = 35.3m/s/343 m/s= 0.103 i really don't know what i am doing wrong...

Can anyone Please help me with this problem? I'm trying to use this formula (velocity = radius * angular velocity), but somehow it's not right Thank You. The diameters of the main rotor and tail rotor of a single-engine helicopter are 7.60 m and 1.02 m, respectively. The respective rotational speeds are 450 rev/min and 4150 rev/min. Calculate the speeds of the tips of both rotors. main rotor? tail rotor? Compare these speeds with the speed of sound, 343 m/s.