Download Conservation of Energy

Active Learning: Potential Energy and Conservation of Energy
rev. 5/12
I Potential Energy
1. A particular force performs the following amounts of work on an object as it goes around closed path
from A to B, then from B to C, then from C to D, and finally from D back to A. Is there a potential
energy associated with this force? Explain.
Point A to Point B
+20 J
Point B to Point C
+10 J
Point C to Point D
-15 J
Point D to Point A
-20 J
2. You have a heavy load on a frictionless cart that you need to get into a truck. You have the choice of
two ramps up into the truck, one 2 times as long as the other.
A. Which ramp will require the most work to raise the load into the truck?
a. The shorter ramp
b. The longer ramp
c. Both the same
B. How much force is required using the longer ramp (compared to the force using the shorter ramp)?
a. 4 times as much force
b. 2 times as much force
c. The same force
d. ½ the force
e. ¼ the force
II Conservation of Energy
1. A 0.25 kg object is pressed against a horizontal spring (k = 120 N/m), compressing the spring 0.2 m.
The object is then released. What is its speed as it leaves the spring? Friction is negligible.
Active Learning: Potential Energy and Conservation of Energy
2. A 100 kg man attached to a 150 m bungee cord (k = 60 N/m) jumps off the Royal Gorge Bridge in
Colorado. The bridge is 290 m above the river. Let the river be zero gravitational potential energy.
A. What is his total energy before he jumps?
B. When he has fallen 200 m, what is his total energy? his total potential energy? his kinetic energy?
C. Set up the conservation of energy equation to solve for the distance he falls before rebounding.
3. A 1300 kg automobile traveling at 22 m/s ascends a hill that is 20 m high. While ascending the hill,
the engine does 320 kJ work while friction does -160 kJ work. Let the bottom of the hill be zero
gravitational potential energy.
A. What is the total mechanical energy at the bottom of the hill?
B. What is the total mechanical energy at the top of the hill?
C. What is the speed at the top of the hill?
Active Learning: Potential Energy and Conservation of Energy
4. The graph below shows U vs x for a 0.60 kg particle confined to move along the x axis. At x = 3.0 m,
the particle’s velocity is +4.6 m/s.
A. Describe the motion of the particle.
B. What is the particle’s kinetic energy at x = 3 m? It’s total mechanical energy?
C. What is the kinetic energy at x = 5 m?
D. Approximately where does the particle turn around?
E. What is the force acting on the particle at the turnaround point?