Two students perform an experiment with a train and a ball. Michelle rides on a atcar pulled at 8.35 m/s by a train on a straight, horizontal track; Gary stands at rest on the ground near the tracks. When Michelle throws the ball with an initial angle of 65.0 above the horizontal, from her point of view, Gary sees the ball rise straight up and back down above a xed point on the ground. (a)Did Michelle throw the ball toward the front of the train or toward the rear of the train? Explain. (b)What was the initial speed of Michelles throw? (c)What was the initial speed of the ball as seen by Gary?
• KeyPoints o UnitofforceandmagnitudeismeasuredinNewtons o Direction=+or- o ObjectofInterest:theobjectbeinganalyzed o Makesuretoaskyourself,“Isitfalling” o NetForce:thesumofforces o Equilibrium:netforce=0 o System:objectofinterestandobjectexertingforcesonit o Contactforce:theforcewheretwoobjectsmeet o Forcediagrams:representforcesexertedonobjectofinterest • ForceDiagrams 1. Useadotforobjectofinterest. F(HAND) 2. Labelobjectofinterest.(PoolBall) 3. Listforcesthatotherobjectsexert