A young girl with mass 40.0 kg is sliding on a horizontal, frictionless surface with an initial momentum that is due east and that has magnitude 90.0 kg · m/s. Starting at ?t? = 0, a net force with magnitude ?F? = (8.20 N/s)?t? and direction due west is applied to the girl. (a) At what value of? ? does the girl have a westward momentum of magnitude 60.0 kg · m/s? (b) How much work has been done on the girl by the force in the time interval from ?t? = 0 to the time calculated in part (a)? (c) What is the magnitude of the acceleration of the girl at the time calculated in part (a)?

Making Sense of the Universe: Chapter 3 4.1 Describing Motion: Examples from Daily Life How do we describe motion Terms used to describe motion: velocity, acceleration, and momentum. Speed – how far something will go in a certain amount of time. Velocity – the speed and direction of something. Acceleration – when there is a change in speed or direction. Acceleration...