Two runners are observed from the ground

PHYSICS · Multi-part · AP · Physics 1: Algebra-based · Work Energy and Power · Work Energy and Power

Problem

Two runners are observed from the ground. Runner 1 has a mass of

60\,\text{kg}

and runs due north at

5.0\,\text{m}\,\text{s}^{-1}

; Runner 2 has a mass of

80\,\text{kg}

and runs due east at

4.0\,\text{m}\,\text{s}^{-1}

. (1) Determine the total translational kinetic energy of the two-runner system as measured by the ground observer. (2) An observer runs alongside Runner 1 at the same speed and in the same direction as Runner 1. Relative to this moving observer, what are the kinetic energies of Runner 1 and Runner 2?

Related theory

Kinetic Energy
Kinetic energy and the work-energy theorem
Work, Energy and Power
Work and Energy

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