# Week 8 (Sep. 30 - Oct. 4)

**Reading:**PSE Chap 5, The laws of motion

**Topics:**the connection between inertia, force, and acceleration, Newton's Axioms (Newton's 3 laws of motion), types of forces

**No quiz this week.**

**Week 8 Homework Problems:**

**Tug of war:**Two astronauts play tug-of war in outer space. Astronaut A has a mass of 200 kg. Astronaut B has a mass of 150 kg. Astronaut A pulls the rope connecting them with a force of 20 Newtons. (a) What is the acceleration of astronaut B? (b) What is the force acting on astronaut A? (c) What is the acceleration of astronaut A? (d) If the rope is 100 meters long when do the astronauts hit each other? Solution.**Ball in gulley:**Consider a long v-shaped gulley cut into an otherwise flat aluminum plate. The bottom of the v-shaped gulley has an angle of 60 degrees. A 1-cm diameter ball-bearing made of steel is dropped into this gulley so that two points on the ball make contact with the walls of the gulley, supporting the ball. (a) First, how far are the two contact points from the bottom of the gulley? (b) Now, what is the normal force exerted by each of the walls of the gulley on the ball? (c) If the angle at the bottom of the gulley were smaller, how would your answers to the previous two questions change? Solution.