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# A man stands in a lift which accelerates upwards. The resultant reaction force on the floor of the lift is

 A) greater than the weight of the man B) less than the weight of the man C) Same as the weight of the man D) Zero

Answer:   A) greater than the weight of the man

Explanation:

The weight of the man mg is acting on the floor. As the lift is moving up with an acceleration, say a, the man too in it is having this acceleration. The force producing this acceleration is ma. By Newton's third law, this force will have an equal reaction pressing the floor equal to ma. Therefore the total resultant reaction on the floor is mg+ma = m(g+a) which is mg, the weight of the man. So (a) is correct.

Subject: Physics

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On the Kelvin scale ,the melting point of ice is

 A) 373K B) 100K C) 273K D) 0 K

Explanation:

Subject: Physics

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Water has maximum density at............

 A) 0 C B) -15 C C) 4 C D) 15 C

Explanation:

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Fish and other aquatic creatures canlive inside a deep frozen pond because

 A) fish are cold-blooded animals B) ice is a bad conductor of heat C) there will always be water just beneath the ice level D) they can adapt themselves to live in ice

Answer & Explanation Answer: C) there will always be water just beneath the ice level

Explanation:

Water has maximum density at $\inline \fn_jvn 4^{0}C$. So at this temperature it sinks down to bottom and stays here. If it cools further, it will become less dense and move up. So while the upper layers can cool enough to form ice, the bottom layers remain as water at $\inline \fn_jvn 4^{0}C$$\inline \fn_jvn \therefore$ (C) is correct.

Subject: Physics

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At what temperature do the Fahrenheit and celcius scales give the same reading?

 A) 212 degrees B) 32 degreees C) -40 degreees D) 0 degreees

Explanation:

$\inline \fn_jvn F=C\times \frac{9}{5}+32$ We want the temperaature when F=C. So substituting C For F, we have C = $\inline \fn_jvn F=C\times \frac{9}{5}+32$

$\inline \fn_jvn \therefore$ C = -40. Thus when C = -40, we have C = F i.e, $\inline \fn_jvn -40^{0}F$

$\inline \fn_jvn \therefore$ (C) is coorrect. i.e,$\inline \fn_jvn -40^{0}C=-40^{0}F$

Subject: Physics

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Pieces of camphor placed on water move about rapidly. This is because of

 A) diffusion B) viscosity C) surface tension D) capillarity