A 45.0 kg girl is standing on a 135 kg plank. The plank, originally at rest, isf

Question

A 45.0 kg girl is standing on a 135 kg plank. The plank, originally at rest, isfree to slide on a frozen lake, which is a flat, frictionlesssurface. The girl begins to walk along the plank at a constantvelocity of 1.52 m/s relative tothe plank. (a) What is her velocity relative to the surface ofice? (b) What is the velocity of the plank relative to the surface ofice?
Thank you so much! (a) What is her velocity relative to the surface ofice? (b) What is the velocity of the plank relative to the surface ofice?
Thank you so much!

Explanation / Answer

    mass of the girl, m1 = 45 kg     mass of the plank, m2 = 135 kg     initial velocity of the girl with respect toplank, U1 = 1.52 m/s     initial velocity of the plank , U2 = 0     final velocity of the ( plank + girl ) = V ( inopposite direction )                             m1 U1 + m2 U2 = ( m1 + m2 ) V                                 45 * 1.52 + 0 = 180 V                                             V = 0.38 m/s ( in opposite direction ) (a)     Velocity of girl relative to ice = U1 - V = 1.52- 0.38 = 1.14 m/s (b)     Velocity of the plank, V = 0.38 m/s (opposite direction )

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