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“Rising to your full potential”
Physics 1 Potential & Kinetic Energy
Name: ____________________________
Date: ___/____/____ Block: ________
Work is found by multiplying Force times displacement in the same direction.
W=F*d
Now we have learned that Work done on an object causes it to gain energy. If the
object has changed its state of motion because of the work done on it, we call it a
change in its Kinetic Energy, or KE.
W = KE
Kinetic Energy depends on the mass of an object, and more importantly on the
velocity of the object.
KE = ½ m v2
Work might also be done on an object to raise it to a higher height. In this case, the
work done is the force opposing gravity times the distance it rises. We can get this
energy back by releasing the object and allowing it to fall. Try it once right now.
The amount of energy an object has because of its location is dependent on the mass
of the object, times the acceleration due to gravity at that point (for us, almost
always -9.8 m/s2), times the height from which it can fall from. The object is said to
have Potential Energy, or PE, because it could be released to do work. Therefore,
PE = mgh
Let’s try a few problems right now to practice working with energy.
1.
You push your seat forward when you get up to leave the class. You push with
a force of 20 N over a distance of 0.2 m.
a)
How much work did you do on the chair?
b)
If the chair has a mass of 2 kg, what is the velocity of the chair after it
leaves your hand?
c)
If the chair encounters a frictional force of 10 N after it leaves your hand,
how far will it slide before coming to a stop?
2.
A baseball player hits a ball with a bat. The bat exerts a force of 1000 N on
the ball over a distance of 0.05 m.
a)
How much work was done on the ball?
b)
3.
A vehicle uses 250,000 J of Energy to accelerate from rest.
a)
If the vehicle has a velocity of 50 m/s now, what is its mass?
b)
4.
How much work was done to lift it?
A piano is lifted 9 meters into the air. If it has a mass of 1000 kg…
a)
How much potential energy does the piano have?
b)
6.
If the vehicle took 100 m to get up to full speed, what force did it exert?
A bookbag is lifted 1 meter. It has a mass of 10 kg.
a)
How much potential energy does it have now?
b)
5.
If the ball has a mass of 0.1 kg, what is the ball’s velocity?
If the piano were lifted to the same height on the moon, where
g = 1.6 m/s2, how much energy would it have then?
To jump, you exert 1400 N of force on the ground. (It exerts 200N back on you)
You apply this force over a distance of 0.3 m as you extend your legs.
a)
How much work have you done?
b)
How high will you rise into the air if your mass is 70 kg?