PhysicsLAB AP Free Response Question
2008 Form B - B1

 
A 70-kg woman and her 35-kg son are standing at rest on an ice rink, as shown above. They push against each other for a time of 0.60 sec, causing them to glide apart. The speed of the woman immediately after they separate is 0.55 m/sec. Assume that during the push, friction is negligible compared with the forces the people exert on each other.
 
 (a) Calculate the initial speed of the son after the push.

 (b) Calculate the magnitude of the average force exerted on the son by the mother during the push.

 (c) How do the magnitude and direction of the average force exerted on the mother by the son during the push compare with those of the average force exerted on the son by the mother? Justify your answer.

 (d) After the initial push, the friction that the ice exerts cannot be considered negligible, and the mother comes to rest after moving a distance of 7.0 m across the ice. If their coefficients of friction are the same, how far does the son move after the push?





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