There is a little flaw in the explanation: One ball down and 4 balls up would perfectly conserve both kinetic energy and momentum, this is no problem, the single ball would be partially reflected. The difference is made by the 4 separate balls: the ball down transfers its complete energy ONLY to the second ball, not to all of them. The 2nd transfers to the third etc.. Only if you glue the four balls together, they would behave as a single mass. But this would also conserve KE and momentum.
Let mass of each ball m, velocity of the ball thrown be u and the velocity of combined system of 4 balls be v then from conservation of momentum mu=4mv From here we get v=u/4 and from conservation of KE ½mu²=½(4m)(v)² From here we get v=u/2 As it is only possible when u=0 So it is not possible to conserve both energy and momentum if all four balls move together.
@@itstanujyadav You have overseen, that the single ball will recoil from the four masses, so it is no problem to conserve both momenta and kinetic energy. If the incoming single ball has the velocity u, then its recoil velocity is -3/5*u, whereas the 4m go in forward direction with 2/5*u. Let us check it: Total momentum before: m*u After (4*2/5-3/5)m*u=m*u Total kin. E before: mu²/2 After: (4*4/25+1*9/25)/2*mu²=1/2mu² Seems to work...
Dear Professor, There is a question which is iching my taught since many days, that why speed of sound is constant??? Even though sound propagate by means of elastic collisions between molicules, speed of sound should depend upon the speed of molecules near the source of sound.
Hey Victor ! In my opinion , the velocity of molicules in air is remarkably high (K.E.=Kb*T) , but logic is that their direction of velocity is completely rendom or say in every direction and those tiny molicules collide million times in a second . >>But a sound signal makes them to vibrate back and forth and creates regions of low and high pressure (sound waves are pressure waves in medium) >> If you may know that in coductors the free electrons moves with very high velocities due to temperature but they moves in random directions , That's why the net current is zero . But wait , if we apply voltage across conductor , this potential difference doesn't affect their previous random velocities but it make all of them to move in a perticular direction but in a slow speed , so we see net current in conductor . Summery:- Sound signal doesn't affect air particle's random high velocities due to temprature but it tries to gave them a net vibration (of any frequencies) in perticular direction and our ear's can sense those vibrations or say pressure waves 🌊 :)
