Download - October 3, 2007
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October 3, 2007
• I have no voice today…• Hence, those dreadful slides, so that I do not need to speak much… or cancel the class…• These slides are in the course web site, under Chapter 8.
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A few reminders
• Assignment 4, due Wednesday, October 10, by 5 pm
• Assignement 5 will be due, Friday, October 19
• Today’s Office Hours: 1 – 4 pm
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Assignment 4
• P. 203 #66 Should be a straightforward application of the Kinetic-Energy Theorem, where you use W = Fd, and you look for F.
• P.203 #74 Use P = W/t and KE Theorem.
• P. 237 #64 similar to P. 236 #52, discussed later today.
• P.236 #38 similar to Example 8-10, discussed next.
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Equation of the day
NCif WEE +=
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where
UKE +=
2
2
1mvK =
forces veconservati-non todue work is NCW
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and
...++= gravityspring UUU
2
2
1kxU spring =
mgyU gravity =
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Potential Energy
• Defined for conservative force as
€
ΔU =U f −U i = −WC
Example: Gravitational Force
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P. 226, Example 8-10
• A block of mass m1 = 2.4 kg is connected to a second block of mass m2 = 1.8 kg. When the blocks are released from rest, they move through a distance d = 0.5 m, at which point m2 hits the floor. Given that the coefficient of kinetic friction between m1 and m2 is mk = 0.45, find the speed of the blocks just before m2 lands.
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P. 236, Problem 52
• A 61-kg skier encounters a dip in the snow’s surface that had a circular cross section with a radius of curvature of 12 m. If the skier’s speed at point A in the Figure is 8.0 m/s, what is the normal force exerted vy the snow on the skier at point B? Ignore frictional forces.
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P. 238, Problem 81
• An ice cube is placed on top of an overturned spherical bowl of radius r as shown in the Figure. If the ice cube slides downward from rest at the top of the bowl, at what angle q does it separate from the bowl? In other words, at what angle does the normal force between the ice cube and the bowl go to zero?
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