(100 points!) A star of radius R1 rotates every 20 days. The star suddenly collapses to a radius R2, which is smaller by a factor of 10000 (R2=R1/10000) without losing mass.

a. What is the new angular velocity of the star? You may assume that the moment of inertia of the star is that of a solid sphere (I=(2/5)mR^2)?

b. What is the ratio of the kinetic energy before and after the collapse (KEf/KEi)?

Zeros that follow non-zeros numbers and are also to the right of a decimal point are significant

Part f - example: finding two forces (part i) two dimensional dynamics often involves solving for two unknown quantities in two separate equations describing the total force. the block in (figure 1) has a mass m=10kg and is being pulled by a force f on a table with coefficient of static friction îľs=0.3. four forces act on it: the applied force f (directed î¸=30â above the horizontal). the force of gravity fg=mg (directly down, where g=9.8m/s2). the normal force n (directly up). the force of static friction fs (directly left, opposing any potential motion). if we want to find the size of the force necessary to just barely overcome static friction (in which case fs=îľsn), we use the condition that the sum of the forces in both directions must be 0. using some basic trigonometry, we can write this condition out for the forces in both the horizontal and vertical directions, respectively, as: fcosî¸â’îľsn=0 fsinî¸+nâ’mg=0 in order to find the magnitude of force f, we have to solve a system of two equations with both f and the normal force n unknown. use the methods we have learned to find an expression for f in terms of m, g, î¸, and îľs (no n).

If the textbook weighs 19.6 newtons on venus, what is the strength of gravity on venus?