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Stress is defined as $\frac{\text{Force}}{\text{Area}}$ [cite: 457].
- Force (Weight) $W \propto \text{Volume} \times \text{density} \propto L^3$
- Area $A \propto L^2$
- $\text{Stress} \propto \frac{L^3}{L^2} \propto L$
- Since $L$ increases by $9$, the stress increases by a factor of $9$[cite: 457].
A synchronous generator with inertia constant $H = 5\,\text{MJ/MVA}$ is rated at $100\,\text{MVA}$. The angular momentum coefficient $M = GH/(\pi f_s)$ used in the swing equation (at $50\,\text{Hz}$) is approximately:
Stored kinetic energy $= H\times S_{rated} = 5\times100 = 500\,\text{MJ}$. Swing equation inertia: $M = \frac{GH}{\pi f_s} = \frac{100\times5}{\pi\times50} = \frac{500}{157.08} \approx 3.18\,\text{MJ·s/rad}$.
The film history of the subcontinent and Pakistan involves several important firsts that students commonly confuse:
- First silent film from Lahore (Punjab): The Daughter of Today (1924), produced by Premier Film Company, directed by Mian Abdur Rasheed Kardar (A.R. Kardar)
- First Punjabi (talkie) film from Lahore: Heer Ranjha (1932), released one year after Alam Ara (1931) — meaning Lahore was almost as fast as Bombay in adopting sound cinema
- First Pakistani film after independence: Teri Yaad (Urdu), released at Perbhat (Sanober) Cinema, Lahore on 7 August 1948 (Eid-ul-Fitr Day). It was a commercial failure but historic as the inaugural film of the new Pakistani industry.
Note: Jugnu (1947) was the last major pre-partition Pakistani film. Khazanchi (1941) was famous for Master Ghulam Haidar's introduction of Punjabi folk music and Baby Noor Jehan as playback singer.
A projectile can achieve the same range $R$ for two angles of projection. If $t_1$ and $t_2$ are the times of flight in the two cases, then:
The two angles giving the same range are $\theta$ and $(90°-\theta)$.
$t_1 = \dfrac{2u\sin\theta}{g}$, $\quad t_2 = \dfrac{2u\cos\theta}{g}$
$t_1 t_2 = \dfrac{4u^2\sin\theta\cos\theta}{g^2} = \dfrac{2u^2\sin2\theta}{g^2} = \dfrac{2R}{g}$
Therefore $t_1 t_2 \propto \mathbf{R}$
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