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At her highest point, a girl on a swing is 7ft above the ground,
and at her lowest point she is 3ft above the ground. What is her maximum velocity?
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At her highest point on the swing, velocity is zero.
Velocity is maximum at her lowest point.
Apply the conservation mechanical energy law
= -
in standard designations. Reduce the factor of mass m in both sides and substitute
the given values. You will get
= 32*7 - 32*3 = 128,
= 2*128 = 256
v = = 16.
ANSWER. The maximum velocity is 16 ft/s at the lowest point.
Solved.
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When we solve this problem, we assume that the mass of the girl
is concentrated in one single point.
Surely, in real life it is not so - - - therefore,
this solution is only APPROXIMATE to real life.
In real life, different points of a body move with different velocities,
but we neglect (!) this fact when solving the problem.