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**1. The problem statement, all variables and given/known data**

A child sits on a freshly oiled, straight stair rail that is frictionless. She has a mass of 25 kg and the rail makes a 40 degree angle with the ground. IF she slides 4.0 m before reaching the bottom, what is her speed there?

**2. Relevant equations**

f=ma

**3. The attempt at a solution**

I did .1(9.8)(sin30)

then i set it equal to .1a=.1(9.8)sin30

and got 4.9 m/s/s but the actual answer is 7.1 m/s/s?

where did i go wrong?