# Week 7

**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

**Lab:**None this week

**Homework Problems: Due October 14 at noon.**

- A hockey puck slides across the ice at a speed of 10 m/s due east. A hockey player strikes the puck with a force of 30 Newtons for 0.01 seconds. The force is directed due west. What is the final velocity of the puck after the force is done acting? What if the force, instead was directed due north? Solution.
- A 1 gram spider is suspended by two threads. One attaches to the wall, the other to the ceiling. If the one attached to the wall is perfectly horizontal, and the one attached to the ceiling makes a 30 degree angle with the ceiling, then what is the tension in each thread? Solution.
- 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.
- What is the acceleration of astronaut B?
- What is the force acting on astronaut A?
- What is the acceleration of astronaut A?
- If the rope is 100 meters long when do the astronauts hit each other? Solution.
- 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.
- First, how far are the two contact points from the bottom of the gulley?
- Now, what is the normal force exerted by each of the walls of the gulley on the ball?
- If the angle at the bottom of the gulley were smaller, how would your answers to the previous two questions change? Solution.

**Quiz: not this week!**