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(11) A 400-kg ice-boat moves on runners on essentially frictionless ice. A steady wind blows, applying a constant force to the sail. At the end of an 8.0-s run, the acceleration is 0.50m/s^2. (a)What was the acceleration at the beginning of run? (b)What was the force due to the wind?

(13) An 59-kg woman stands in an elevator. What force does she exert on the floor of the elevator under the following conditions? (a) The elevator rises with a constant velocity of 2.0 m/s. (c)The elevator goes down with a constant velocity of 4.0 m/s. (e) While going down, the elevator decelerates at 1.5 m/s^2.

I want to ask that what is the diff. between x=xo+1/2(vo+v)t and s=1/2(u+v)t. what is the meaning of xo and x?

And which equ will given during the exam?