## Physics: Principles with Applications (7th Edition)

The momentum in the horizontal direction will be conserved. Let the positive direction be the direction in which the tackler was originally moving. $$(110 kg)(2.5 m/s) + (82 kg)(-5.0 m/s) = (110 kg + 82 kg)v$$ Solve for v = -0.70 m/s. The negative sign means they are moving in the direction that the halfback was originally running.