Physics
Assertion (A) : A body when weighed by a spring balance, weighs slightly less in air than in vacuum.
Reason (R) : This is so because of upthrust of air on body.
- both A and R are true and R is the correct explanation of A
- both A and R are true and R is not the correct explanation of A
- assertion is false but reason is true
- assertion is true but reason is false
Answer
both A and R are true and R is the correct explanation of A
Explanation
Assertion (A) is true because in air, there is a buoyant force (upthrust) acting upward on the object, which reduces the apparent weight. In a vacuum, there is no upthrust, so the object shows its true weight.
Reason (R) is true because the upthrust from the surrounding air causes the body to appear lighter in air than in vacuum and hence Reason explains the Assertion.
Related Questions
The density of ice is 0.92 g cm-3 and that of sea water is 1.025 g cm-3. Find the total volume of an iceberg which floats with it's volume 800 cm3 above water.
A weather forecasting plastic balloon of volume 15 m3 contains hydrogen of density 0.09 kg m-3. The volume of an equipment carried by the balloon is negligible compared to it's own volume. The mass of empty balloon alone is 7.15 kg. The balloon is floating in air of density 1.3 kg m-3. Calculate : (i) the mass of hydrogen in the balloon, (ii) the mass of hydrogen and balloon, (iii) the total mass of hydrogen, balloon and equipment if the mass of equipment is x kg, (iv) the mass of air displaced by balloon and (v) the mass of equipment using the law of floatation.
Assertion (A) : A bucket filled with water is heavier till it is immersed in water in well.
Reason (R) : The effect of upthrust is that the weight of body immersed in liquid appears to be lighter than its actual weight.
- both A and R are true and R is the correct explanation of A
- both A and R are true and R is not the correct explanation of A
- assertion is false but reason is true
- assertion is true but reason is false
Assertion (A) : An iron nail sinks in water, but floats in mercury.
Reason (R) : The density of iron is equal to density of mercury but greater than water.
- both A and R are true and R is the correct explanation of A
- both A and R are true and R is not the correct explanation of A
- assertion is false but reason is true
- assertion is true but reason is false