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Q:

A balloon filled with hydrogen will

A) continue going upwards uninterrupted B) reach a particular height and remain floating
C) burst after reaching some height D) reach a particular height and start coming down
 
Answer & Explanation Answer: B) reach a particular height and remain floating

Explanation:

It will stop at a height where the weight of the balloon with contents is equal to the weight of air displaced by it, i.e , when the upthrust is equal to the downthrust. The question of bursting will depend on how much difference of pressure inside and outside , the material of the balloon can withstand. It is assumed the balloon is filled with a lighter than air gas like hydrogen or helium.

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Q:

A bucket of water is hung from a spring balance. A piece of iron is suspended in the water without touching the sides or touching the bottom of the bucket. The reading of the spring balance

A) will increase B) will decrease
C) does not change D) varies with the increase of depth of the immersion of the iron piece
 
Answer & Explanation Answer: A) will increase

Explanation:

When the piece of iron is lowered into the water, the water level in the bucket increases. And so the pressure at the bottom of bucket also increases. Thus the total thrust at the botto also increases. Therefore the spring balance reading increases.

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Q:

A piece of ice is floating in water kept in a beaker. When all the ice melts the level of water will

A) first rise and then fall B) fall
C) remain the same D) rise
 
Answer & Explanation Answer: C) remain the same

Explanation:

The submerged portion of the ice on melting shrinks a little in volume. so the level of water goes down a little.But this is just made up by the water added by the melting of upper portion. Addition is equal to the Shrinkage. Hence level is unchanged.

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Q:

When a steel ball is placed on the surface of mercury, it does not sink because

A) of the surface tension of mercury B) mercury is a semisolid
C) of the high viscosity of mercury D) the density of mercury is greater than that of steel
 
Answer & Explanation Answer: D) the density of mercury is greater than that of steel

Explanation:

A solid sinks in a liquid if its density is greater than that of the liquid. if less, it floats

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Q:

The force that keeps a body in a circular motion called 

A) the centripetal force B) the centrifugual force
C) the frictional force D) all the above
 
Answer & Explanation Answer: A) the centripetal force

Explanation:

without this centripetal force, circular motion is not possible. It acts radially towards the centre and if this force is removed there will be no circular motion but the revolving body will fly off at a tangent.

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Q:

Frictional force acts in 

A) the same direction as the motion B) the opposite direction of the motion
C) all the directions D) upward direction
 
Answer & Explanation Answer: B) the opposite direction of the motion

Explanation:

It is to overcome this opposite frictional force , that  we have to apply the needed force to make the body move

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Q:

When a bullet is fired from a gun 

A) the gun moves forward B) the gun jumps up
C) the gun does not move D) the gun recoils with the same momentum as the bullet
 
Answer & Explanation Answer: D) the gun recoils with the same momentum as the bullet

Explanation:

Newton's III law involved

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Q:

It is more difficult to walk on ice than on a concrete road because 

A) there is very little friction between the ice and feet pressing it B) ice is soft when compared to concrete
C) there is more friction between the ice and feer D) None of these
 
Answer & Explanation Answer: A) there is very little friction between the ice and feet pressing it

Explanation:

It is the friction between the feet and the ground that helps us to walk. Without this friction we would slip and fall

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