A block of mass m = 4.4 kg, moving on frictionless surface with a speed v i = 9.

Question

A block of mass m =                 4.4 kg, moving on frictionless                 surface with a speed vi = 9.2 m/s makes a perfectly                 elastic collision with a block of mass M at rest. After the                 collision, the 4.4 kg block                 recoils with a speed of vf = 2.5 m/s.  In the                 figure, the mass M is closest to:   
                               A)  21                 kg     B)  5.6                 kg     C)  7.7                 kg     D)  12                 kg     E)  4.4                 kg A block of mass m =                 4.4 kg, moving on frictionless                 surface with a speed vi = 9.2 m/s makes a perfectly                 elastic collision with a block of mass M at rest. After the                 collision, the 4.4 kg block                 recoils with a speed of vf = 2.5 m/s.  In the                 figure, the mass M is closest to:   

Explanation / Answer

Ek1+Ek2 = Ek1'+Ek2'

m1(v1)^2+m2(v2)^2 = m1(v1')^2+m2(v2')^2
4.4*9.2^2 + 0 = 4.4*2.5^2 + m2(v2')^2

now you have two equations with two unknowns.

7.68kg. is answer... so C) 7.7 kg

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