Work

1
2009 Physics Nobelists
2
Work Kinetic Energy Skills
1.Compute the work done by a constant force in
1D. Get the sign right! 2. Compute the work done
by a constant force in 2D. Take dot product
correctly! 3. Understand that work done by a
non-constant force in 1D is area under the F vs x
curve. Compute for easy F(x) examples. 4.
Memorize that work done by a spring is And/or
that potential energy of a spring is 5.
Memorize that work done by gravity is 6. Find
the change in the speed of a particle using the
work-energy thm.
3
Potential Energy Skills

1. Understand which forces are conservative, and how
   to solve problems (velocities, spring
   compressions, height of projectile etc.) using
   conservation of energy.
2. By accounting for lost energy in friction,
   solve similar problems with a frictional force.
3. Find direction and magnitude of force from a
   potential energy diagram (1D).

• Other important skills
• Find apparent weight
• Find centripetal force

4
What is the magnitude of the normal force at the
top of a loop the loop, if the box is released
from h5R/2 ?
A 0 B mg C 2mg D 4mg E 6mg
5
What is the tangential acceleration at the bottom
of a loop the loop?
A 0 B g C 5g D 5/2 g E -g
6
What is the tension in the rod at 90,IF THAT IS
THE HIGHEST POINT IN THE ARC?
A lt 0 (rod is being compressed) B 0 C gt 0
What if, as before, the high point of the arc is
at 120? C, positive, as tension provides the
centripetal force.