Conservation of Mechanical Energy

Roller Coaster Dynamics Lab: Conservation of Energy

Roller Coaster Dynamics Lab: Conservation of Energy

Physics - Std 11: Verification of Mechanical Energy Conservation

Investigate the **Conservation of Mechanical Energy** ($ME$). In ideal systems, the sum of Potential Energy ($PE$) and Kinetic Energy ($KE$) remains constant: $ME = PE + KE = \text{constant}$.

Mission Briefing: Key Equations & Formulas

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Energy Formulas ($g = 9.8 \text{ m/s}^2$):
  • **Potential Energy ($PE$):** $$ PE = m \cdot g \cdot h $$
  • **Kinetic Energy ($KE$):** $$ KE = \frac{1}{2} m \cdot v^2 $$
Conservation Principle (Ideal):

$$ PE_{\text{start}} + KE_{\text{start}} = PE_{\text{end}} + KE_{\text{end}} $$

Work-Energy Theorem (Real World):

Work done by non-conservative forces ($W_{nc}$, e.g., friction) equals the change in mechanical energy: $$ W_{nc} = \Delta ME = ME_{\text{end}} - ME_{\text{start}} $$

Experiment 1: Ideal System Verification (Frictionless)

Simulate a frictionless track. The cart starts from rest ($v_{start}=0$) at height $h_{start}$.

Start Height ($h_1$)
10 m
End Height ($h_2$)
0 m
Total $ME$
98 J
$PE_{start} = KE_{end}$ ($v_{end}$ = 14.0 m/s)

Experiment 2: Work-Energy Challenge (Non-Ideal System)

The cart starts at $h_1$, passes through a friction zone, and stops at $h_{end}$. Calculate $v_{end}$ or $W_{nc}$.

$h_{start}$
10.0 m
$h_{end}$
4.0 m
$W_{nc}$ (Friction Loss)
-147.0 J
Verify $v_{end}$ (using $W_{nc}$) and $W_{nc}$ (using $\Delta ME$).
Result Status
The Conservation Law (Ideal):

In the absence of non-conservative forces (like friction or air drag), energy freely converts between $PE$ and $KE$. A roller coaster reaches its maximum speed ($KE$) at its lowest point ($h=0$), where its $PE$ is minimum.

Real-World Energy Loss (11th Std)

Work Done by Friction:

In a real system, the initial total energy is always greater than the final total energy. The difference is the work done against friction, which is always negative (energy loss). $$ W_{\text{friction}} = ME_{\text{final}} - ME_{\text{initial}} $$

Power:

The rate at which mechanical energy is transferred or converted is called Power ($P$). The average power is $$ P_{\text{avg}} = \frac{W}{\Delta t} $$.

Zero Work Condition:

Work is zero when the force applied is perpendicular to the displacement (e.g., gravity doing work on a cart moving on a horizontal surface).

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