Collision Problem - A gain of kinetic energy?

[eurekameh]

In Fig. 9-64, block A (mass 1.1 kg) slides into block B (mass 2.9 kg), along a frictionless surface. The directions of velocities before and after the collision are indicated; the corresponding speeds are vAi = 5.6 m/s, vBi = 2.2 m/s, and vBf = 4.9 m/s. What is velocity vAf (including sign, where positive denotes motion to the right)?

I believe that this collision is inelastic and not elastic, because kinetic energy is lost to other forms of energy, correct? And so momentum is conserved, kinetic energy is not?

I conserved momentum and found the final velocity of block A. However, when I calculated the kinetic energy before and after the collision, I found that the kinetic energy after the collision is greater than the kinetic energy before the collision. How is this possible?

Edit: No external forces are present.

 

[eczeno]

can you show us the work you did.

 

[eurekameh]

Momentum before = Momentum after
(1.1)(5.6) + (2.9)(2.2) = (1.1)(vAf) + (2.9)(4.9)
I found vAf.
But when I calculated the kinetic energy before and after the collision, I got an increase in kinetic energy, as in : kinetic energy before collision < kinetic energy after collision.

Kinetic energy before collision:
(1/2)(1.1)(5.6)^2 + (1/2)(2.9)(2.2)^2 = 24.3 J.

Kinetic energy after collision, using vAf = -1.52, found when conserving momentum:
(1/2)(1.1)(-1.52)^2 + (1/2)(2.9)(4.9)^2 = 36.1 J.

My question is this: Is it possible to have an increase in kinetic energy when there are no apparent external forces acting on the system of the two colliding blocks? Or are my calculations faulty? Or is the problem itself faulty?
Thanks for the responses.

 

[eczeno]

well, we seem to have an impossible situation here. and in fact we do. if you look at the change in KE of B, it is bigger than the whole of A's KE coming in. this is impossible. these numbers do not correspond to a possible physical situation.