1. - The capacity to do work.
- Energy causes changes to the object and/or to its
surroundings.
- Human and animals need energy from the food.
- Vehicles needs fuel in order to move.
- Therefore, energy and work are inseparable.
3. • It is energy by the virtue of object’s motion.
• Energy in motion
• Example:
• A rolling boulder from the mountainside
• A running bus
• A flying arrow
• Unit used is Joules and also joules is equal to kg.m2s2
4. • To measure the kinetic energy of a body, you have to consider its mass
and speed. In symbol,
Kinetic energy depends on the mass of object as well as the speed.
-basketball has more mass
than a tennis ball, therefore
basketball will have a
greater kinetic energy than
the tennis ball though they
are rolled at the same
speed.
- Basketball with same mass is
rolled at different speed. Basketball
A is rolled at a greater speed than
of Basketball B, therefore
Basketball will have more KE than
B. Possible that the KE will be times
four than the other if rolled with a
speed twice as that of the other.
Different Mass but same speed Different speed but same mass
5. Which will have a more KE?
bus will have more KE than the car with the same speed, since
bus had more mass than the car.
A moving car A moving bus
6. 1. A car is travelling at a velocity of 10 m/s and it has a mass of 250 Kg.
Compute its kinetic energy?
G: v= 10 m/s; m = 250 kg; KE = ?
S: KE = ½ mv2
KE = ½ x (250 kg)(10m/s)2
KE = ½ x (250 kg)(100 m2/s2)
KE = ½ x (25000 kg.m2/s2)
KE = 25000 kg.m2s2 ÷ 2
A: KE = 12,500 kg.m2s2 or 12, 500 J
7. 2. A man is transporting a trolley of mass 6 Kg and having Kinetic
energy of 40 J. Compute its Velocity with which he is running?
G: m = 6 kg; KE = 40 J; v = ?
S: v = 2𝐾𝐸/𝑚
v = 2(40 𝐽)/𝑘𝑔
v = 80 𝐽/6𝑘𝑔
v = 13.3 𝐽/𝑘𝑔
A: v = 3.65 m/s
8. • Object’s at rest can have the capacity to do work.
• Example;
• Hollow block at the edge of a two-storey house
• A volcano
• Stretched bowstring
They have stored energy that can perform work when time requires.
9. – energy due to object’s position relative to a
certain height
– like with the case of compressed spring or stretched
rubber
– inherent in all substances like petrol, wood, and
plants.
10.
11. SAMPLE PROBLEM
• A crane lifts a 75kg mass a height of 8 m. Calculate the gravitational
potential energy gained by the mass (g = 9.8 m/s2).
G: m = 75 kg; g = 9.8 m/s2; h = 8 m; PE = ?
S: PEg = mgh
PEg = (75 kg)(9.8 m/s2)(8 m)
PEg = 5,880 kg.m2/s2
A: PEg = 5,880 J
12. 2. An owl has a mass of 4.00 kg. It dives to catch a mouse, losing
800.00 J of its GPE. What was the starting height of the owl, in
meters?
G: m = 4.00 kg; PEg = 800.00 J; g = 9.8 m/s2; h = ?
S: h = PE/mg
h = 800.00 J/(4.00 kg)(9.8 m/s2)
h = 800.00 J/39.2 kg.m/s2)
A: h = 20.41 m
13. • Example: when using a slingshot to hit the target, it needs to put a small
rock into the leather pad, pull it and release. Upon release, the small
rock is launched into the air hitting the target. The kinetic energy came
from the stored energy in the stretched rubber.
• Elastic PE can be stored in any stretched or compressed object like
springs and rubber bond.
14. Formula for Elastic PE
X = distanced stretched or compressed
K = elastic constant or also called as force constant (unit is N/m)
15. SAMPLE PROBLEM!!!
1. If the force to stretch a spring is given as k = (100 N/m), then what
is the potential energy of the spring if it is stretched 2 meters from
rest?
G: k = 100 N/m ; x = 2 m; Pee =?
S: PEe = kx2
= (100 N/m) (2 m)2
= (100 N/m) (4 m2)
A: PEe = 400 J
16. 2. A spring has an extension of 20 cm. Calculate the elastic potential energy
stored in the spring (k = 100 N/m).
G: x = 20 cm x (1m/100 cm) = 0.2 m
k = 100 N/m Pee = ?
S: PEe = kx2/2
= (100 N/m)(0.2 m)2
= (100 N/m)(0.4 m2)
A: PEe = 4 J
