ENERGY A BODY HAS BECAUSE OF ITS

POSITION OR CONDITION

P.E.= EP.E.= Ep p = mgh= mghG.P.E. = weight x height

KINETIC ENERGY (E k) = ½ mv2

=KE mv2

2

POTENTIAPOTENTIAL ENERGYL ENERGY

ENERGY A BODY HAS BECAUSE OF ITS

POSITION OR CONDITION

P.E.= EP.E.= Ep p = mgh= mghG.P.E. = weight x height

POTENTIAL ENERGYEp or p.e. is the potential energy an

object has because of its height.“The higher an object is lifted, the

greater its p.e.”“The greater the mass of an object the

greater its p.e.”

the gain in p.e. = work done Ep = W

EXAMPLEEXAMPLEWhat is the p.e. of a book of What is the p.e. of a book of mass mass 1200 g1200 g, resting on a shelf , resting on a shelf 2 m2 m above the ground? above the ground?

p.e. = mghp.e. = 1.2kg x 10m/s/s x 2m p.e. = 12.0 N x 2 mp.e. = 24 N-meter or Joulesp.e. = 24 N-meter or Joules

SAMPLE PROBLEM:

A hiker weighing 680 N climbs 40 m up a hill. Calculate the gravitational potential energy gained at the top of the climb. Ep= mgh

Ep = 680 N x 40 m

= 27,200 N-m

or 27.2 KJ

P.E.= Ep= mgh

1. Calculate the p.e. of a 40 kg iron bar raised 1 m. (g = 10m/s/s)

2. Calculate the p.e. of a 65 kg boulder resting at 22 m above the road.

3. A 200 g jar falls from a height 1.5 m onto the floor. Calculate the p.e. of the jar before the fall.

1. Calculate the p.e. of a 40 kg iron bar raised 1 m. 400 N-m or 400J

2. Calculate the p.e. of a 65 kg boulder resting at 22 m above the road. 14,300 N-m or 14.3 KJ

3. A 200 g jar falls from a height 1.5 m onto the floor. Calculate the p.e. of the jar before the fall. 3 J

ANSWERS

Remember: W = F x d where the lifting force is m x g

(F= ma)(m = mass, g = acceleration

due to gravity)

gain in p.e. = work done gain in p.e. = work done EpEp = W = W

Putting these formulae together: Gain in Potential energy= work done Gain in Potential energy= work done

liftinglifting

Ep = WEp = W

= lifting force x distance lifted = lifting force x distance lifted (height)(height) Ep = F x d (h)Ep = F x d (h)

= weight force x distance lifted = weight force x distance lifted Ep = Fg x d (h) Ep = Fg x d (h) (g = 10N/kg)(g = 10N/kg)

= mass of object x g x distance lifted= mass of object x g x distance lifted

Ep = mgh

KINETIC ENERGY (E k) = ½ mv2

=KE mv2

2

KINETIC ENERGYKINETIC ENERGY• Kinetic energy EkKinetic energy Ek or k.e. is the or k.e. is the energy that an object has because it energy that an object has because it is is movingmoving•The The unit of measureunit of measure for k.e. is for k.e. is joulejoule•The The greater the speed the greater the greater the speed the greater the

k.e. of the objectk.e. of the object•The greater the mass of a moving The greater the mass of a moving object, the greater the k.eobject, the greater the k.e. of the . of the objectobject

What is the Ek of an arrow weighing 25 gm traveling at 25m/s?

What is the Ek of an arrow weighing 25 gm traveling at 25m/s?Answer:

k.e. = ½ mv2 = ½ x .025kg x 25m/s2

= ½ x 0.025kg x 625m/s = (0.5) 15.625

= 7.8125 Nm but 1 Nm = 1J

= 7.8125 J

Potential Energy = Weight x Height (P.E. = w x h) or Ep= mgh Kinetic Energy = ½ Mass x Velocity2 (K.E.= 1/2mv2)

weight = mg Units: Energy = joules (J) Weight = newtons (N)

Mass = kilograms (kg) Velocity = m/s

Height = meters (m)

Gravity constant = 9.8m/sec/sec

1km = 1000m1km = 1000m 1kg= 1000g1kg= 1000g 1hr= 3,600sec1hr= 3,600sec

Work = joules

Energy cannot be created nor destroyed. Energy is converted from one form to

another.