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The microwave oven has become a standard appliance in many kitchens, mainly because it offers a fast way of cooking food. Yet, some homeowners believe that the ovens are still not completely safe. Microwaves, therefore, should not be a standard appliance until they have been carefully researched and tested.
Sub-Questions:
1 The conclusion of the passage is that, because of safety concerns, more research and testing ought to be done before microwaves become standard household appliances. If, however, research and testing are ineffective means of discerning safety problems (as choice C says), then research and testing would be irrelevant. This criticism seriously weakens the conclusion. So choice C is the correct answer.
2 If many microwave ovens have been found to leak radioactive elements (as choice D says), then the conclusion that microwaves should not be standard appliances until they are more carefully researched and tested is further strengthened because more safety concerns need to be addressed. So, choice E is the correct answer.
In hydrogen and hydrogen-like (one-electron) atoms, orbitals with the same \(n\) are degenerate — 2s and 2p have the same energy (energy depends only on \(n\)). The statement that 2s energy is less than 2p is only true for multi-electron atoms (due to penetration and shielding). Hence option (3) is wrong for hydrogen-like atoms.
A particle is thrown vertically upward. Its speed at half the maximum height is $10\text{ m/s}$. The maximum height attained is ($g = 10\text{ m/s}^2$):
Let maximum height $= H$. At height $H/2$, velocity $= 10\text{ m/s}$.
Using $v^2 = u^2 - 2g\cdot\dfrac{H}{2}$: $100 = u^2 - gH$
At max height: $0 = u^2 - 2gH \Rightarrow u^2 = 2gH$
Substituting: $100 = 2gH - gH = gH \Rightarrow H = \dfrac{100}{10} = \mathbf{10\text{ m}}$
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