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.

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

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.

Equation of the day

NCif WEE +=

where

UKE +=

2

2

1mvK =

forces veconservati-non todue work is NCW

and

...++= gravityspring UUU

2

2

1kxU spring =

mgyU gravity =

Potential Energy

• Defined for conservative force as

€

ΔU =U f −U i = −WC

Example: Gravitational Force

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.

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.

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?