Summary Jee physic work power energy formula sheet

WORK, POWER, ENERGY

WORK POWER AND ENERGY
Work : Work is done by the force if point of application of force is displaced.


F
ds
Work done by the force is the dot product of force and displacement or work done is the product of
mganitude of displacement and component of force along displacement.
r uur
dw  Fds  Fds cos    Fcos   ds

dw  0 if 0    90o
dw  0 if 90o    180o
dw = 0 if   90o
Work done by variable force for displacement S1 to S2 is given by F
S2 O s1 s2 s
w   F.ds ; F is force along displacement
S1

Work done by the variable force is the area below the curve drawn between component of force along
displacement and magnitude of displacement.
The S.I. unit of work is joule others are erg, ev, kwh.
a. 1 joule = 107 erg
b. 1 erg = 10–7 joule
c. 1 ev = 1.6 ×10–19J
d. 1 kwh = 3.6×106 joule
e. 1 joule = 6.25×1012 Mev
Power : The rate of doing work is power
r uur
F.dx dw dk
P  
dt dt dt
rr
P  F.v  ins tan tan eous power delivered
Unit of power is joule sec–1 or watt.
1 hp = 746 watt.
Instantaneous power delivered in case of projectile is give by
P

P   mg ˆj .  u cos iˆ   u sin   gt  ˆj
O t
  mg  u sin   gt 
 mg 2 t    mgu sin  
Power delivered at the maxium height of projectile is zero.



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