Suppose a clay model of a koala bear has a mass of 0.25 kg and slides on ice at a speed of 0.85 m/s. It runs into another clay model, which is initially motionless and has a mass of 0.45 kg. Both being soft clay, they naturally stick together. Friction on ice can be neglected.

vf = 0.3 m/s

Explanation:

Assuming no external forces act during the collision, total momentum must be conserved.

The initial momentum is due to the koala bear moving at 0.85 m/s:

p₀ = m₁ * v₀₁ = 0.25 kg. 0.85 m/s = 0.21 N. m

As the collision is inelastic, both masses stick together, so the final momentum can be written as follows:

p₁ = (m₁ + m₂) * vf₁₂ = 0.7 kg * vf₁₂ = 0.21 N. m (as p₀ = p₁,

Now, we can solve for the common speed of both masses after the collision, as follows:

vf₁₂ = 0.21 N. m / 0.7 kg = 0.3 m/s (in the same direction that v₀₁).