# Week 16

**Reading:**PSE Chap 14 gravity

**Topics:**Newton's law of gravity, Kepler's laws, planetary motion,

**Lab:**None.

**Homework Problems: Due on Monday, Dec. 5 at noon.**

**Automobile problem (****solution****):**A 1500 kg automobile has a wheel base (distance between wheels) of 3 meters. The center of mass of the automobile is on at the center line at a point 1.2 meters behind the front axle. Find the force exerted by the ground on each wheel.**Ladder problem (****solution****):**A ladder weighing 400 N and a length 10 meters is placed against a smooth (frictionless) vertical wall. A person weighing 800 N stands on the ladder 2 meters from the bottom as measured along the ladder. The foot of the ladder is 8 meters from the bottom of the wall. The floor exerts a friction force, f, that keeps the ladder from sliding out. Calculate the normal force exerted by the wall, the friction force exerted by the floor, and the normal force exerted by the floor on the ladder.**Meteor problem (****solution****):**A dangerous meteor flies past the Earth. It passes a distance of 5 earth radii from the surface of the earth. What is the acceleration of the meteor at this distance?**Mass of Jupiter (****solution****):**Io, a small moon of Jupiter, has an orbital period of 1.77 days and an orbital radius of 4.22 x 10^5 km. From this data, determine the mass of Jupiter.**Optional calculus/challenge problem:**A very thin 10 meter long lead rod is curved into a semi-circle. The total mass of the bar is 100 kg. A small lead ball of mass 1 kg is placed at the center of the semi-circle, equidistant from every point on the bar. What is the gravitational force exerted by the bar on the ball? Hint: you will need to sum up the force of gravitational attraction on the ball from each little segment of the rod by integrating.

**Quiz: None.**