Physics 218: Mechanics Instructor: Dr. Tatiana Erukhimova

Lecture 23

ENERGY DIAGRAMS

Stable vs. Unstable Equilibrium Points

The force is zero at both maxima and minima but…– If I put a ball with no velocity there would it stay?– What if it had a little bit of velocity?

A particle moves along the x-axis while acted on by a single conservative force parallel to the x-axis. The force corresponds to the potential-energy function graphed in the Figure. The particle is released from rest at point A.

a)What is the direction of the force on the particle when it is at point A?

b) At point B?

c) At what value of x is the kinetic energy of the particle a maximum?

d) What is the force on the particle when it is at point C?

e) What is the largest value of x reached by the particle during its motion?

f) What value or values of x correspond to points of stable equilibrium?

g) Of unstable equilibrium?

Quiz

Quiz

A 2.00-kg block is pushed against a spring with negligible mass and force constant k=400 N/m compressing in 0.220 m. When the block is released, it moves along a frictionless, horizontal surface and then up a frictionless incline with slope 370. a) What is the speed of the block as it slides along the horizontal surface after having left the spring? b) How far does the block travel up the incline before starting to slide back down?

Have a great day!

Reading: Chapter 9Hw: All Chapter 9 problems and exercises