A 100 kg mass is blown apart into a 90.0 kg piece and a 10.0 kg piece. After the blast, the two masses are moving apart with a relative velocity of 100 m/s. The velocity of the 10.0 kg mass after the explosion is 90.0 m/s. The total kinetic energy of the two masses after the explosion is

  • Option 1)

    63,200 J.

  • Option 2)

    45,000 J.

  • Option 3)

    30,400 J.

  • Option 4)

    23,400 J.

 

Answers (2)

OPTION 2: 45,OOO J

Centre of mass remains at rest. So its speed is zero.

(m1v1+m2v2) / (m1+m2) = 0

m1v1 + m2v2 = 0

m1 =90kg

m2= 10kg

v2= 90m/s

v2- v1= 100m/s

v1=10m/s

Total KE = 1/2 x m1x v1^2 +1/2x m2x v2^2

By substituting the values

Total KE = 45000J

 

take it the reverse way.. like two mases colliding to form one mass and after collision the complete mass is at rest. so

m1v1+m2v2/m1+m2=0

solve for v2 and substitue it in the next equation u will get the answer

 

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