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(1)

Work, Energy and Power formulae

www.vaxasoftware.com Work of a constant force

(Force is parallel to displacement) (Work of force of friction)



cos

x

F

W





x

F

W





x

F

W





_FRIC



Kinetic energy 2

2

1 v

m

E

_K



Gravitational potential energy

(Near a planet surface)

E

P



m

g

h

Gravitational potential energy

r

m

M

E

_P





G

Elastic potential energy 2

2

1 x

k

E

_P





Mechanical (total) energy

_E

_M

_

_E

_K

_

_E

_P Mechanical energy conservation

_

_

₀

M

E

(all forces are conservative)

NCF

M

W

E





(there are non-conservative forces) Inelastic collision

v

m

v

m

v

m

p

_BEFORE



_AFTER



)

(



₁ ₁



₂ ₂



₁



₂



Elastic collision 2 2 1 1 2 2 1 1

'

m

v

m

v

m

v

m

v

p

_BEFORE



_AFTER













After K Before K

E



Power m u m m

P

F

v

t

W

P

;







Unit conversions 1 cal = 4.184 J

1 J = 0.239 cal

1 HP = 736 W (nevertheless there are many definitions)

1 kW·h = 3.6 · 106_J

Symbol Description S.I. Unit

W

Work

J

E

K Kinetic energy

J

E

P Potential energy

J

E

M Mechanical energy

J

F

Force

N

x  Displacement

m

r

Distance

m

h

Hight

m

M, m

Mass

kg



Force-displacement angle

°

v

Speed

m/s

v

m Mean speed

m/s

g

Gravitational acceleration(9.8 m/s2 _{in Earth surface)}

_m/s

2

G

Gravitational constant: 6.67·1011

_N·m

2

_/kg

2

k

Elastic constant of the spring

N/m

p

Momentum

kg·m/s

P

m Mean power

W