Two friends, Al and Jo, have a combined mass of 168 kg. At anice skating rink th

Question

Two friends, Al and Jo, have a combined mass of 168 kg. At anice skating rink they stand close together on skates, at rest andfacing each other, with a compressed spring between them. Thespring is kept from pushing them apart because they are holdingeach other. When they release their arms, Al moves off in onedirection at a speed of 0.82 m/s, while Jomoves off in the opposite direction at a speed of 1.4 m/s. Assuming that friction is negligible, findAl's mass.
_______kg
Two friends, Al and Jo, have a combined mass of 168 kg. At anice skating rink they stand close together on skates, at rest andfacing each other, with a compressed spring between them. Thespring is kept from pushing them apart because they are holdingeach other. When they release their arms, Al moves off in onedirection at a speed of 0.82 m/s, while Jomoves off in the opposite direction at a speed of 1.4 m/s. Assuming that friction is negligible, findAl's mass.
_______kg

Explanation / Answer

        mA +mJ = 168 kg According to conservation of momentum we have      0 = mAvA- mJvJ      mAvA = mJvJ        mAvA=  (-mA+168 kg)vJ       mA(vA + vJ) = 168 *vJ        mA= 168 *vJ / (vA +vJ)               = 168 * 1.4 / (0.82 + 1.4 )               = 105.94 kg      mAvA = mJvJ        mAvA=  (-mA+168 kg)vJ       mA(vA + vJ) = 168 *vJ        mA= 168 *vJ / (vA +vJ)               = 168 * 1.4 / (0.82 + 1.4 )               = 105.94 kg        mA= 168 *vJ / (vA +vJ)               = 168 * 1.4 / (0.82 + 1.4 )               = 105.94 kg

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