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Q:

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
Q:

A disk and a sphere of same radius but different masses roll on two inclined planes of the same altitude and length. Which one of the two objects gets to the bottom of the plane first ?

A) Depends on their masses B) Sphere
C) Disk D) Both reach at the same time
 
Answer & Explanation Answer: B) Sphere

Explanation:

Time does not depend on mass, else

  => is least for 'sphere' and

hence least time is taken by sphere.

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Q:

A potentiometer wire is 100 cm long and a constant potential difference is maintained across it. Two cells are connected in series first to support one another and then in opposite direction. The balance points are obtained at 50 cm and 10 cm from the positive end of the wire in the two cases. The ratio of the emf's is :

A) 3:4 B) 5:4
C) 5:1 D) 3:2
 
Answer & Explanation Answer: D) 3:2

Explanation:

In series : E1 + E2 = K(50)

In parallel : E1 - E2 = K(10)

E1 + E2 / E1 - E2 = 5/1

=> E1/E2 = 3/2

The emf's are in the ratio of 3:2.

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Q:

What is the maximum velocity with which a body of mass 'm' must enter a vertical loop of radius 'R'so that it can complete the loop ?

A)    B) gR   C)    D)   

A) A B) B
C) C D) D
 
Answer & Explanation Answer: C) C

Explanation:

To complete the vertical loop, the minimum speed required at the lowest point  =  .

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Q:

Which of the following group of elements are diamagnetic ?

A) Argon, copper, silver B) Hydrogen, argon, copper
C) Oxygen, copper, silver D) Hydrogen, oxygen, Argon
 
Answer & Explanation Answer: A) Argon, copper, silver

Explanation:
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Q:

At the Curie temperature, the ferromagnetic materials get converted into

A) Diamagnetic materials B) Non-magnetic materials
C) Paramagnetic materials D) None of the others
 
Answer & Explanation Answer: C) Paramagnetic materials

Explanation:
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