Two gliders, A (550 g) and B(350 g), are held together by a string which compres

Question

Two gliders, A (550 g) and B(350 g), are held together by a string which compresses a spring between the gliders. As shown, the masses are traveling at 0.5m/s. A very quick, but not so safety-conscious physics student burns the string between the masses after which mass B is seen to be traveling at 2.1 m/s. Find the velocity of mass A?

Did the kinetic energy of the system grow, shrink or stay the same during this process? If it grew, where did the energy come from? If it shrank, where did the energy go?

Finally estimate the spring constant of the spring.

Explanation / Answer

FROM CONSERVATION OF MOMENTUM

(0.55)(VA)+(0.35)(2.1) = (0.55+0.35) (0.5)

SO, VELOCITY OF A IS VA = - 0.518 m/s

Change in KE is 1/2(m1u1^2+m2u2^2) - 1/2((m1+m2)*v^2)

1/2(.55*(0.518)^2+0.35(2.1)^2)-1/2(0.9)*0.5^2

Initial KE - Final KE = 0.73 J

So, KE Shrank...

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