Work Work Work Work Work
Work done is considered positive, except when done by this force.
Friction or Gravity
How much potential energy does a 500g egg have, when raised 15 meters above the ground?
73.5 J
What is work?
Work is what happens when a force causes a displacement.
Work is how a force changes an object's energy
40J, because energy is conserved.
THE Moon
Earth
How much work is done in pushing a TV set a horizontal distance of 2m with an average force of 40N?
W = Fd = (40N)(2m) = 80J
While swinging on a swing at a play ground, you have your greatest kinetic energy at what point in your swing?
At the very bottom
How is energy different from work?
Energy is an object's capacity (potential) to exert a force. Work is the act of using that energy to exert a force.
A 5kg mass is held 6m above the ground. Relative to the ground, it has a potential energy of __________
30 J
Phobos, Deimos
Mars
A 1000kg car and a 2000kg car are hoisted to the same height for concurrent oil changes. Compare work required to lift each car.
The car with twice the mass will require twice the force to lift, and therefore requires twice the work.
How much power is expended if you lift a 50 N rock 10 meters in 2 seconds?
250 Watts
D A I L Y
O
U
B
L
E
doo doo doo doo doo doo doo
A powerlifter raises 150kg weight a height of 2.7m. What is its GPE?
3969 J
Triton, Nereid, Naiad, Proteus
Neptune
A car is traveling with a kinetic energy of 1300J when it suddenly slams on its brakes. It skids to a stop in 7.22m. What was the force of friction?
180M
If a rocket doubles its speed after takeoff, by how much does its kinetic energy change?
4x
Describe 2 different ways you can increase the power expended during an exercise.
1)Increase the work done during the exercise
2)Decrease the time for the exercise
An Olympic lifter has lifted a 165kg weight 1.7m, and holds it still for 2 seconds for the judges to count the lift as complete. How much work do they do on the weight during these 2 seconds?
NONE - no displacement means no work
Ganymede, Callisto, Io, Europa
Jupiter
A 2000 kg car is traveling at 4 m/s, when it begins to apply its brakes, supplying a 400N frictional force. This force does work to reduce the car's kinetic energy to 0J. What is the car's displacement by the time it skids to a stop?
40m
How much kinetic energy does a pitcher have to give to a 1.2kg baseball to send it speeding towards home plate with a velocity of 40m/s?
960 J
Describe a situation in which energy is NOT conserved.
Any outside force (friction) changing the total energy of an object.
At a track meet, a high-jumper leaps with an initial vertical velocity of 5m/s. If all of their kinetic energy is converted into gravitational potential energy, how high do they jump?
1.28 m
Miranda, Puck, Oberon, Titania
Uranus