Rolling friction is caused by ____ from the following?
Answer: A
Rolling friction arises from non-elastic effects.
The wheel and the surface deform slightly at the contact, and the deformation does not recover all its energy as the contact moves on - the hysteresis loss. This is why rolling friction is far smaller than sliding friction, and why hard, well-inflated tyres roll more easily.
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Which of the following physical quantities have the same dimensions
Answer: A
Momentum and impulse share dimensions.
Impulse is force times time and momentum is mass times velocity: \[[\mathrm{Ft}] = \mathrm{MLT^{-2}\cdot T} = \mathrm{MLT^{-1}},\qquad [\mathrm{mv}] = \mathrm{M\cdot LT^{-1}} = \mathrm{MLT^{-1}}\] They must agree, since the impulse–momentum theorem says one equals the change in the other.
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The number of base SI units is
Answer: B
There are seven base SI units.
They are the metre, kilogram, second, ampere, kelvin, mole and candela, for length, mass, time, electric current, temperature, amount of substance and luminous intensity. Every other SI unit is derived from these.
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