Homework Help: physics

Posted by tanya on Wednesday, December 2, 2009 at 7:57pm.

a sled slides down a frictionless hill. if the sled starts from rest at the top, its speed is 7.5 m/s.

a.) on a second run , the sled starts with a speed of 1.5 m/s at the top.. will it end with less than 9 m/s, 9 m/s, or more than 9 m/s

b.) find the speed of the sled at the bottom of the hill after the second run

physics - drwls, Wednesday, December 2, 2009 at 9:04pm
Before trying to answer (a), let's do (b).

Due to the starting kinetic energy, the KE at the bottom will be increased from
(1/2)M(7.5)^2 to (1/2)M[(1.5)^2 + (7.5)^2] = (1/2)M(58.5) = (1/2)M(7.64)^2

The velocity at the bottom in the second case will be 7.64 m/s.

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