110 likes | 209 Views
Bell Ringer. Brown, Jones and Smith are a doctor, a lawyer, and a teacher. The teacher, who is an only child, earns the least money. Smith, who married Brown's sister, earns more than the lawyer. What is each man's job?. Work-Kinetic Energy Theorem.
E N D
Bell Ringer • Brown, Jones and Smith are a doctor, a lawyer, and a teacher. The teacher, who is an only child, earns the least money. Smith, who married Brown's sister, earns more than the lawyer. What is each man's job?
Work-Kinetic Energy Theorem • An object's kinetic energy can be changed by an outside force (including gravity) doing work on it. • POSITIVE work (either more force or more distance) → increasing kinetic energy (speeding up, giving energy to the object) • NEGATIVE work (force and distance in opposite directions) → decreasing kinetic energy (slowing down, taking energy away from the object)
A baseball has a mass of 0.35 kg and an initial velocity of 45 m/s. In order for it to come to rest in the catcher’s glove, how much work does the glove need to do? Is this positive or negative work?
“Before” • A penny with a mass of 0.002 kg is dropped from rest from a height of 10 m. → What kind of energy does the penny start with? → How much initial energy does the penny have?
“After” • The 0.002 kg penny falls from the 10 m height to the ground and has a velocity of 14 m/s right before it hits the ground.→ What kind of energy does the penny have? → How much final energy does the penny have?
Work? • Use the Work-Kinetic Energy Theorem to determine how much work was done on the penny as it fell. • What force did this work? Is it positive or negative work?
“Before” • A 75 kg pole vaulter leaves the mat at a velocity of 10.8 m/s. → What kind of energy does the pole vaulter have? → How much initial energy does the pole vaulter have?
“After” • The same 75 kg pole vaulter reaches a height of 6 m. → What kind of energy does the pole vaulter have at the highest point of his trajectory? → How much final energy does the pole vaulter have?
Work? • Use the Work-Kinetic Energy Theorem to determine how much work was done on the pole vaulter as he jumped. • What force did this work? Is it positive or negative work?
A farmer has a fox, goose and a bag of grain, and one boat to cross a stream, which is only big enough to take one of the three across with him at a time. If left alone together, the fox would eat the goose and the goose would eat the grain. How can the farmer get all three across the stream?