A 45.0-kg girl is standing on a 144-kg plank. The plank, originally at rest, is

Question

A 45.0-kg girl is standing on a 144-kg plank. The plank, originally at rest, is free to slide on a frozen lake, which is a flat, frictionless surface. The girl begins to walk along the plank at a constant velocity of 1.44 m/s to the right relative to the plank. (Let the direction the girl is moving in be positive. Indicate the direction with the sign of your answer.)

A 45.0-kg girl is standing on a 144-kg plank. The plank, originally at rest, is free to slide on a frozen lake, which is a flat, frictionless surface. The girl begins to walk along the plank at a constant velocity of 1.44 m/s to the right relative to the plank. (Let the direction the girl is moving in be positive. Indicate the direction with the sign of your answer.) What is her velocity relative to the surface of ice? m/s What is the velocity of the plank relative to the surface of ice? m/s

Explanation / Answer

a)the velocity relative to the surface of ice is u = 1.44 m/s

b)we know from the relation

m1u1 + m2u2 = (m1 + m2) x V

or V = [m1u1 + m2u2/m1 + m2]

where m1 = 45.0 kg,u1 = 1.44 m/s,m2 = 144 kg,u2 = 0 and V is the velocity of the plank relative to the surface of ice.

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