# Week 11

**Reading:**PSE Chap 8, Potential energy and conservation of energy

**Topics:**conservative and nonconservative forces, conservation of energy, energy diagrams, e=mc squared,

**Lab:**

**Homework Problems: Due Tuesday, Oct 31.**

**Work on a particle.****Solution****.**A 4.0 kg particle is moving along the x-axis. Its position varies according to x(t) = t + 2.0 * t^3. x(t) is in meters and t is in seconds. (i) Find the kinetic energy at any time, t. Hint: use calculus. (ii) Find the acceleration and the force acting on it at time t. (iii)Find the power delivered to the particle at time t. (iv) Find the work done on the particle in the time interval between 0 and 2 seconds.**Spring gun:****Solution****.**A spring gun is used to launch a stainless steel ball straight up into the air. The spring constant is 10 Newton per centimeter. The spring is compressed 2 cm. Assume the ball weights 100 grams and that the spring itself is massless and frictionless. What is the muzzle velocity of the ball at the moment it leaves the gun? Hint: the change is kinetic energy is equal to the -net- work done on the ball. There are two forces doing work on the ball. Now: how would your answer change if the gun is aimed at a 45 degree angle? Is the muzzle velocity the same?**Pushed block:**A block of mass 2.5 kg is pushed 2.2 m along a frictionless horizontal table by a constant 16.0 N force directed at 25 degrees below the horizontal. Determine the work done by (a) the applied force (*31.9 Joules*), (b) the normal force exerted by the table (*0 Joules*), (c) the force of gravity (*0 Joules*) and (d) the net force on the block (*31.9 Joules*).

**Quiz:**On Monday, Oct. 23, covering week 10