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Please Compute… A man cleaning a floor pulls a vacuum cleaner with a force of magnitude 50 N at an angle of 30 degrees to the horizontal. Calculate the.

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Presentation on theme: "Please Compute… A man cleaning a floor pulls a vacuum cleaner with a force of magnitude 50 N at an angle of 30 degrees to the horizontal. Calculate the."— Presentation transcript:

1 Please Compute… A man cleaning a floor pulls a vacuum cleaner with a force of magnitude 50 N at an angle of 30 degrees to the horizontal. Calculate the work done by the force on the vacuum as the vacuum is displaced 3.0 m to the right

2 Please Consider… The gravitational force exerted by the Sun on the Earth holds the Earth in an orbit around the Sun. Let us assume that the orbit is perfectly circular. The work done by this gravitational force during a short time interval in which the Earth moves through a displacement in its orbital path is (a) zero (b) positive (c) negative (d) impossible to determine

3 Please Consider… When a punter kicks a football, is he doing any work on the ball while his toe is in contact with it? Is he doing any work on the ball after it loses contact with his toe? Are any forces doing work on the ball while it is in flight?

4 Please Consider… A force acting on a particle varies with position, as shown. Calculate the work done by the force as the particle moves from x = 0 to x = 6.0 m

5 Please Compute… A 6.0-kg block initially at rest is pulled to the right along a horizontal, frictionless surface by a constant horizontal force of 12 N. Find the speed of the block after it has moved 3.0 m

6 Please Consider… One bullet has twice the mass of a second bullet. If both are fired so that they have the same speed, which has more kinetic energy? What is the ratio of the kinetic energies of the two bullets?

7 Please Consider… A car traveling at an initial speed v slides a distance d to a halt after its brakes lock. Assuming that the car’s initial speed is instead 2v at the moment the brakes lock, estimate the distance it slides

8 Please Compute… A 6.0-kg block initially at rest is pulled to the right along a horizontal surface by a constant horizontal force of 12 N. Find the speed of the block after it has moved 3.0 m if the surfaces in contact have a coefficient of kinetic friction of 0.15

9 Please Consider… In most circumstances, the normal force acting on an object and the force of static friction do zero work on the object. However, the reason that the work is zero is different for the two cases. Explain why each does zero work

10 Please Consider… A woman wishes to load a refrigerator onto a truck using a ramp. She claims that less work would be required to load the truck if the length L of the ramp were increased. Is her statement valid?

11 Let Us Compute… A 50.0-kg marathon runner runs up the stairs to the top of Chicago’s 443-m-tall Willis Tower, the tallest building in the United States. To lift herself to the top in 15.0 minutes, what must be her average power output?

12 For You to Consider… An older model car accelerates from rest to speed v in 10 seconds. A newer, more powerful sports car accelerates from rest to 2v in the same time period. What is the ratio of the power of the newer car to that of the older car? (a)0.25 (b) 0.5 (c) 1 (d) 2 (e) 4


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