WORK, POWER, ENERGY Flashcards
define work
when a force is applied on a body and it covers some displacement in the direction of force.
at which angle, work done is zero
at 90°
at which angle is work done maximum and positive
0°
at which angle is work done half of the maximum value
60°
at which angle is work done maximum and negative
180°
what are the SI units of work
joule
base units of work
Nm or kgm^2/s^2
for conservative field, work done along closed path is
zero
1 J is equal to how many ergs
10^7
what is the CGS unit of work
erg
for cyclic Fd graph, work done will be
0
give examples of conservative fields
gravitational field, electric field, magnetic field, elastic field and nuclear force
for non-conservative field, work done along closed path is
not zero
give examples of non-conservative field
frictional force, drag force, air resistance, tension and normal reaction
define energy
ability of body to do work
formula for potential energy
P.E = mgh
formula for absolute potential energy
P.E = -GMm/R
formula for kinetic energy
1/2mv^2
formula for elastic potential energy
1/2kx^2
potential energy if movement is upwards will be
-mgh
potential energy if movement is downward will be
+mgh
negative P.E means
increasing potential energy
positive P.E means
decreasing P.E
in the presence of air resistance, what will be the formula relating P.E & K.E if movement is upward
K.E = P.E + Wf
1/2mv^2 = mgh + hf
in the absence of air, what will be the formula relating P.E & K.E
loss in P.E = gain in P.E
mgh(h1-h2) = 1/2mv^2
in the absence of air, what will be the formula for velocity
√ 2g (h1-h2)
what is the formula relating K.E & momentum
K.E = p^2 / 2m
in the presence of air resistance, what will be the formula relating P.E & K.E if movement is downward
P.E = K.E + Wf
mgh = 1/2mv^2 + fh
shortcut for finding percentage change in K.E
% K.E = 2p + p^2/100
define escape velocity
the minimum velocity which is required to throw a body outside the earth’s gravitational field is called escape velocity
formula for escape velocity
v = √ 2GM/R
on which factors escape velocity does NOT depend
size and mass of object
angle of projection
what is the value of escape velocity for earth
11km/s
on which factors does escape velocity depend
on the size and mass of planet only
what is the work energy principle?
work done on a body always changes its kinetic energy
the stopping distance d is directly proportional to
the square of velocity
define power
the rate of doing work is called power
formula of power for lift
P = mgh/T
1 erg is equal to how many joules
10^-7 Joules
SI unit of power is
Watt
the famous unit of power is called
horsepower
1 horsepower is equal to how many watts?
746 W
1 kWh is equal to how many joules
3.6 x 10^6
1 calorie is equal to how many joules
4.18
1 eV is equal to how many joules
1.6 x 10^-19
1 Joule is equal to how many eV
6.25 x 10^18 eV
1 Joule is equal to how many ergs
10^7
