6.) A mass of 0.2 kg attached to a spring oscillates onafrictionless horizontal surface. Its motion is described by x=0.05 m cos(50 rad/s t + 1.57 rad).Find a) the frequency andperiod;b) the maximum velocity and acceleration; c) the forceconstant andthe mechanical energy.

7.) A traveling wave in a string of linear density 0.01kg permeter is described by the wave function

y = 0.02 m sin(50 rad/m x - 1750 rad/s t).Find a) thedirectionof propagation; b) the wave length and the period; c) thewave speedand the tension in the string.

8.) A copper wire of cross section area 0.04cm^{2} andlength 1.2 m is heated from the room temperature20 ^{0}C to40 ^{0}C. Find a) the change of itslength in the process;b) the force needed at each end if it werestretched at T = 20^{0}C with the same extension. ( Thecoefficient of linearexpansion for copper is 1.7 x 10^{-5}/K . The Young'smodulus for copper is 1.1 x 10^{11}N/m^{2} .)