CP Jumping to the Ground. A 75.0-kg man steps off a platform 3.10 m above the ground. He keeps his legs straight as he falls, but his knees begin to bend at the moment his feet touch the ground; treated as a particle, he moves an additional 0.60 m before coming to rest. (a) What is his speed at the instant his feet touch the ground? (b) If we treat the man as a particle, what is his acceleration (magnitude and direction) as he slows down, if the acceleration is assumed to be constant? (c) Draw his free-body diagram. In terms of the forces on the diagram, what is the net force on him? Use Newton’s laws and the results of part (b) to calculate the average force his feet exert on the ground while he slows down. Express this force both in newtons and as a multiple of his weight.
CP Jumping to the Ground. A 75.0-kg man steps off a platform 3.10 m above the ground. He keeps his legs straight as he falls, but his knees begin to bend at the moment his feet touch the ground; treated as a particle, he moves an additional 0.60 m before coming to rest. (a) What is his speed at the instant his feet touch the ground? (b) If we treat the man as a particle, what is his acceleration (magnitude and direction) as he slows down, if the acceleration is assumed to be constant? (c) Draw his free-body diagram. In terms of the forces on the diagram, what is the net force on him? Use Newton’s laws and the results of part (b) to calculate the average force his feet exert on the ground while he slows down. Express this force both in newtons and as a multiple of his weight.
CP Jumping to the Ground. A 75.0-kg man steps off a platform 3.10 m above the ground. He keeps his legs straight as he falls, but his knees begin to bend at the moment his feet touch the ground; treated as a particle, he moves an additional 0.60 m before coming to rest. (a) What is his speed at the instant his feet touch the ground? (b) If we treat the man as a particle, what is his acceleration (magnitude and direction) as he slows down, if the acceleration is assumed to be constant? (c) Draw his free-body diagram. In terms of the forces on the diagram, what is the net force on him? Use Newton’s laws and the results of part (b) to calculate the average force his feet exert on the ground while he slows down. Express this force both in newtons and as a multiple of his weight.
Gayle runs at a speed of 3.20 m/s and dives on a sled, initially at rest on the top of a frictionless snow-covered hill. After she has descended a vertical distance of 5.00 m,
her brother, who is initially at rest, hops on her back and together they continue down the hill. What is their speed at the bottom of the hill if the total vertical drop is
med
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15.0 m? Gayle's mass is 49.5 kg, the sled has a mass of 5.45 kg and her brother has a mass of 30.0 kg.
m/s
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A 0.4 kg ball is thrown vertically upward with an initial speed of 15 m/s as it leaves the throwers hand. During its motion, a 50 N air friction acts on the ball. How high will the ball go?
A student is on the roof of the SP building, 15.0 m above the ground. Your physics instructor, who is 163 cm tall, is walking alongside the building at a constant speed of 0.35 m/s. If you wish to drop an egg on your instructors head, where should the instructor be when you release the egg? Assume the egg is in free fall and air friction is “negligible”.
Chapter 4 Solutions
University Physics with Modern Physics (14th Edition)
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