Question

Two figure skaters, one weighing 625 𝑁 and the other 725 𝑁, push off against each other on frictionless ice. (a) If the heavier skater travels at 1.50 𝑚/𝑠, how fast will the lighter one travel? (b) How much kinetic energy is “created” during the skaters’ maneuver, and where does this energy come from? 

Answer 1

$m_1=625/9.8=63.8\ (kg)$

$m_2=725/9.8=74\ (kg)$

(a) $m_1v_1=m_2v_2\to v_2=m_1v_1/m_2=$

$=74\cdot1.5/63.8=1.74\ (m/s)$

(b) $KE=m_1v_1^2/2+m_2v_2^2/2=63.8\cdot1.74^2/2+$

$+74\cdot1.5^2/2\approx180\ (J)$

Energy is obtained by converting chemical energy in muscles into their mechanical energy.