# Chapter 5:Energy¶

## Example 5.2 , Page no:31¶

In [1]:
import math
from __future__ import division

#initialisation of variables
F=60; #force in lb
s=10; #distance inft

#CALCULATIONS
W=F*s; #3calculating weight

#RESULTS
print"Weight in ft.lb =",round(W);

Weight in ft.lb = 600.0


## Example 5.3 , Page no:31¶

In [2]:
import math
from __future__ import division

#initialisation of variables
F=2000; #force in lb
s=80; #distance inft

#CALCULATIONS
W=F*s; #calculating weight

#RESULTS
print"Weight in ft.lb =",round(W);
print"Potential Energy in ft.lb =",round(W);

Weight in ft.lb = 160000.0
Potential Energy in ft.lb = 160000.0


## Example 5.4 , Page no:31¶

In [3]:
import math
from __future__ import division

#initialisation of variables
g=9.8; #gravitational constant in m/sec square
h=1.5; #height in m
m=2; #mass in kg

#CALCULATIONS
W=m*g*h; #calculating weight

#RESULTS
print"Weight in Joule =",round(W,3);
print"Potential Energy in Joule =",round(W,3);

Weight in Joule = 29.4
Potential Energy in Joule = 29.4


## Example 5.5 , Page no:31¶

In [4]:
import math
from __future__ import division

#initialisation of variables
g=9.8; #gravitational constant in m/sec square
m=2; #mass in kg

#CALCULATIONS
W=m*g; #calculating weight

#RESULTS
print"Weight in Newton =",round(W,3);

Weight in Newton = 19.6


## Example 5.7 , Page no:31¶

In [5]:
import math
from __future__ import division

#initialisation of variables
F=150; #F in lb
s=10; #distance in ft
t=5; #time in sec

#CALCULATIONS
P=(F*s)/t; #Power in ft.lb/sec
p1=P/550;

#RESULTS
print"Power in hp =",round(p1,3);

Power in hp = 0.545


## Example 5.8 , Page no:32¶

In [6]:
import math
from __future__ import division

#initialisation of variables
s=80; #height in m
p=20; #power of hoist in hp
m=500; #weight in kg
g=9.8; #gravitational constant in m/sec square
e=0.8; #efficiency = 80 percent

#CALCULATIONS
F=m*g; #Force in Newton
P=e*p*746; #calculating power in watt
t=(F*s)/P; #calculating time required

#RESULTS
print"Time required in sec =",round(t,3);

Time required in sec = 32.842


## Example 5.9 , Page no:32¶

In [7]:
import math
from __future__ import division

#initialisation of variables
v=10; #velocity in min/hr
p=80; #power required in hp

#CALCULATIONS
v1=v*1.47; #converting v to ft/sec
P1=p*550; #converting P to ft.lb/sec
F=P1/v1; #calculating resistive force required

#RESULTS
print"Resistive force required in lb =",round(F,3);

Resistive force required in lb = 2993.197


## Example 5.10 , Page no:32¶

In [8]:
import math
from __future__ import division

#initialisation of variables
p=1;#power output in hp
p=1*746; #power output in Watt using 1hp = 746Watt
F=300; #Force in Newton

#CALCULATIONS
v=p/F; #calculating v in m/sec using P=F*v

#RESULTS
print"Velocity in m/sec =",round(v,3);

Velocity in m/sec = 2.487


## Example 5.11 , Page no:32¶

In [9]:
import math
from __future__ import division

#initialisation of variables
m=1000; #mass in kg
v=20; #velocity in m/sec

#CALCULATIONS
KE=(m*v*v)/2; #calculating kinetic energy using KE=1/2*(m*v*v)

#RESULTS
print"Kinetic Energy in Joule =",round(KE);

Kinetic Energy in Joule = 200000.0


## Example 5.12 , Page no:32¶

In [10]:
import math
from __future__ import division

#initialisation of variables
m=1; #mass in kg
KE=1; #Knetic Energy in Joule

#CALCULATIONS
v=math.sqrt((2*KE)/m); #calculating velocity in m/sec using KE=1/2(m*v*v)

#RESULTS
print"Velocity in m/sec =",round(v,3);

Velocity in m/sec = 1.414


## Example 5.13 , Page no:32¶

In [11]:
import math
from __future__ import division

#initialisation of variables
v=15; #velocity in ft/sec
w=128; #weight in lb
g=32; #g in ft/sec square

#CALCULATIONS
m=w/g; #calculating m in slugs
KE=(1/2)*(m*v*v); #calculating KE in ft.lb

#RESULTS
print"Kinetic Energy in ft.lb =",round(KE,3);

Kinetic Energy in ft.lb = 450.0


## Example 5.14 , Page no:32¶

In [12]:
import math
from __future__ import division

#initialisation of variables
w=2500; #weight in lb
v=40; #velocity in mi/hr

#CALCULATIONS
m=w/g; #calculating mass in slugs
v=40*1.47; #converting velocity in ft/sec
KE=(1/2)*(m*v*v); #calculating Kinetic energy in ft.lb

#RESULTS
print"Kinetic Energy in ft.lb =",round(KE,3);

Kinetic Energy in ft.lb = 135056.25


## Example 5.15 , Page no:33¶

In [13]:
import math
from __future__ import division

#initialisation of variables
h=7-3; #height above ground in ft
g=32; #g in ft/sec square

#CALCULATIONS
v=math.sqrt(2*g*h); #calculating velocity in ft/sec since PE=KE

#RESULTS
print"Velocity in ft/sec =",round(v,3);

Velocity in ft/sec = 16.0


## Example 5.16 , Page no:33¶

In [14]:
import math
from __future__ import division

#initialisation of variables
v=20; #velocity in m/sec
g=9.8; #g in m/sec square
h=200; #height in m

#CALCULATIONS
diff=(v*v)/(2*9.8*200); #calculating Final KE/Initial PE
diff1=(1-diff)*100;

#RESULTS
print"Percent of initial PE lost =",round(diff1,3);

Percent of initial PE lost = 89.796


## Example 5.17 , Page no:33¶

In [15]:
import math
from __future__ import division

#initialisation of variables
w=3; #weight in lb
v=15; #velocity in ft/sec
g=32; #g in ft/sec square

#CALCULATIONS
s=(1/24); #s in ft
F=(w*v*v)/(2*g*s); #calculating force exerted in lb

#RESULTS
print"Force exerted in lb =",round(F,3);

Force exerted in lb = 253.125


## Example 5.18 , Page no:33¶

In [16]:
import math
from __future__ import division

#initialisation of variables
g=9.8; #g in m/sec square
h=2; #height in m
F=100; #force in Newton
s=15; #s in m
v=2; #velocity in m/sec
m=30; #mass in 30 kg

#CALCULATIONS
W=F*s; #calculating work in Joule
delKE=(1/2)*(m*v*v); #calculating change in KE in Joule
delPE=m*g*h; #calculating change in PE in Joule
Wf=W-delKE-delPE; #calculating work in Joule
Ff=Wf/s; #calculating frictional force in Newton

#RESULTS
print"Frictional Force in Newton =",round(Ff,3);

Frictional Force in Newton = 56.8


## Example 5.19 , Page no:33¶

In [17]:
import math
from __future__ import division

#initialisation of variables
t=1; #time in sec
m=4*10**9; #m in kg
c=3*10**8; #velocity of light in m/sec

#CALCULATIONS
E=m*c*c; #calculating Energy in Joule using Einstein's equation: E=m*c*c
P=E/t; #calculating Power output in Watt

#RESULTS
print"Power Output in Watt =",round(P,3);

Power Output in Watt = 3.6e+26


## Example 5.20 , Page no:33¶

In [18]:
import math
from __future__ import division

#initialisation of variables
P=10**8; #power in Watt
t=60*60*24; #t in seconds for 1 day
c=3*10**8;

#CALCULATIONS
E=P*t; #calculating energy in Joule using E=P*t
m=E/(c*c); #calculating m in kg using Einstein's equation:E=m*c*c

#RESULTS
print"Mass in kg =",round(m,6);

Mass in kg = 9.6e-05