Conceptual Questions - Chapter 4 Work Energy and Power 11th Science Guide Samacheer Kalvi Solutions - SaraNextGen [2024-2025]

Updated On May 15, 2024

By SaraNextGen

Conceptual Questions
Question 1.
A spring which in initially in un-stretched condition, is first stretched by a length $\mathrm{x}$ and again by a further length $\mathrm{x}$. The work done in the first case $\mathrm{W}_1$ is one third of the work done in second case $\mathrm{W}_2$. True or false?
Answer:
The amount of work done to stretching distance $\mathrm{x}$
$
\mathrm{W}_1=\frac{1}{2} k x^2 \quad \therefore \quad k=\frac{2 \mathrm{~W}_1}{x^2}
$
Total work done in stretching the spring through a distance $2 \mathrm{x}$ is
$
\begin{aligned}
& \mathrm{W}_2=\frac{1}{2} k(2 x)^2 \\
& \mathrm{~W}_2=\frac{1}{2}\left(\frac{2 \mathrm{~W}_1}{x^2}\right) 4 x^2=4 \mathrm{~W}_1
\end{aligned}
$
Extra work required to stretch the additional $\mathrm{x}$ distance is
$
\begin{aligned}
& \mathrm{W}=\mathrm{W}_2-\mathrm{W}_1=4 \mathrm{~W}_1-\mathrm{W}_1=3 \mathrm{~W}_1 \\
& \mathrm{~W}=\mathrm{W}_2-\mathrm{W}_1=4 \mathrm{~W}_1-\mathrm{W}_1=3 \mathrm{~W}_1 \\
& \therefore \quad \mathrm{W}_1=\frac{1}{3} \mathrm{~W} \\
&
\end{aligned}
$
Hence it is true
Question 2.
Which is conserved in inelastic collision? Total energy (or) Kinetic energy?
Answer:
In inelastic collision total energy is only conserved but kinetic energy is not conserved. A part of kinetic energy is converted into some other form of energy such as sound, heat energy.
Note: The linear momentum is also conserved.
Question 3.
Is there any net work done by external forces on a car moving with a constant speed along a straight road?
Answer:
If the car moves at constant speed, then there is no change in its kinetic energy. It implies that if there is no change in kinetic energy then there is no work done by the force on the body provided its mass remains constant.
Question 4.
A car starts from rest and moves on a surface with uniform acceleration. Draw the graph of kinetic energy versus displacement. What information you can get from that graph?
Answer:

A car starts from rest and moves with uniform acceleration. The graph between kinetic energy and displacement, is a straight line.
The slope of $\mathrm{KE}$ and displacement graph gives net force acting on the car to keep the car with uniform
acceleration.

Question 5.
A charged particle moves towards another charged particle. Under what conditions the total momentum and the total energy of the system conserved?
Answer:
Coulomb force is acting in between the charged particles Internal force is a conservative force. If no external forces act or the work done by external forces is zero then the mechanical energy of the system and also total linear momentum also remains constant.