J Calculating Friction: Determining Energy Lost in Sled Ramp Descent

[bobsmith76]

Homework Statement

A sled weighing 70kg, going at 14 m/s, slides down a ramp 3 m high. It's final velocity is 15.6 m/s. How much energy was lost due to friction?

Homework Equations

.5mv_i² + mgh = .5mv_f² + x

where x = joules of energy for friction

The Attempt at a Solution

step 1 .5(70)(14²+70(9.8)(3) = .5(70)(15.6² + x

step 2 6860 + 2058 = 8570 + x

step 3 6860 + 2058 - 8570 = x

step 4 401 = x

The books says the answer is 74

 

[Doc Al]

I'd say that you were correct. (8570 is a typo, though.)