a. Joule
b. True
c. Energy associated with the motion of the object is called Kinetic energy. A body of mass m and moving with velocity v has a kinetic energy
$K=\frac {1}{2}mv^2$
d. Now,
$K=\frac {1}{2}mv^2$
If mass is double and velocity is made halved
$K_1=\frac {1}{2} 2m (v/2)^2 =\frac {1}{2} K$
So Kinetic energy get halved
e. False
f. Workdone is zero
g. Power is defined as the rate of doing work. The SI unit of power is watt. 1 W = 1 J/s
h. Energy can not be created or destroyed.It can be transformed from one form to another
Column A (Energy Conversion) |
Column B (Converters) |
Chemical energy into Mechanical energy |
Electric Generator |
Heat energy into Mechanical engine |
Electric Motor |
Mechanical energy into Electrical energy |
Car engine |
Electrical energy to Mechanical energy |
Steam engine |
Light energy into electrical energy |
Electric bulb |
Electrical energy into light energy |
Solar Cell |
Angle |
30 |
45 |
60 |
90 |
Work done |
? |
? |
? |
? |
Workdone is given by
$W= Fd cos \theta$
Where $\theta$ is the angle between force and displacement
$cos 30 = \frac {\sqrt {3}}{2}$
$cos 45 = \frac {1}{\sqrt {2}}$
$cos 60 = \frac {1}{2}$
$cos 90 = 0$
So,answer is
Height from earth(m) |
10m |
? |
? |
2m |
Potential energy(J) |
? |
? |
500J |
? |
Kinetic energy(J) |
? |
1000J |
? |
? |
Mechanical energy (J) |
? |
? |
? |
? |
This can be easily solved using below formula
$PE =mgH$ , Mechanical Energy= PE + KE
Mechanical Energy remains constant during the Free Fall
Across
2. The scientist with whom unit of power is named
5. The kinetic energy of the body depends on mass and this quantity
7. The energy possessed by the car moving on the road
8. The Bigger unit of power
9. Work and power are these quantities
Down
1. The work done by the earth on the satellite moving in circular path
3. Solar water heater converts this energy into heat energy
4. The gravitation potential energy is present because of this
6. In hydroelectric power house, the potential energy of the water is finally transformed to this energy
Crossword Solution
Across
James,velocity,kinetic,kilowatt,scalar
Down
Zero,light,Position,electrical
Power of electric bulb = 60 W
= 0.1 kW.
Time used, t = 8 h
$Energy = power \times \text{time taken}$
$= 0.1 \times 8 $
$= 0.8 kWh$
= 0.8 'units'.
The energy consumed by the bulb is 0.8 'units'.
Energy possessed = PE= $mgH= 10 \times 10 \times 2 = 200 J$
Entire PE is converted to KE when the child reaches bottom
So
KE = PE
$\frac {1}{2} mv^2 = mgH$
or $H= \frac {v^2}{2g} = \frac {16}{2 \times 9.8} = .816 m$
(c)
$KE_1 = \frac {1}{2} mv^2 $
$KE_2 = \frac {1}{2} m(3v)^2 =9 \times \frac {1}{2} mv^2$
$KE_1 : KE_2 = 1 :9 $
Workdone is given by
$W= Fd cos \theta$
Where $\theta$ is the angle between force and displacement
$cos 60 = \frac {1}{2}$
Hence $W= 10 \times 3 \times \frac {1}{2} = 15 J$