Page 36 - Physics - XI

Q10. What is the S.I. unit of weight?
Ans. S.I. unit of weight is newton.

Q11. Why does weight of a body change from place to place?
Ans. Weight, W = mg, g the acceleration due to gravity changes from place to place and hence the weight
of a body changes from place to place.
Q12. How can you measure the weight of a body?
Ans. The weight of a body can be measured by a spring balance.

Q13. State the principle of a spring balance.
Ans. It works on Hooke's law, i.e. extension produced in the spring balance is directly proportional to the
gravitational force acting on it within the elastic limit.

Q14. Can we measure mass of a body by a spring balance?
Ans. Yes, only at the place of calibration of its scale.
Q15. How can you measure inertial mass?
F
Ans. Inertial mass is measured by the relation, m = . By knowing the force F acting on a body which
a
produces acceleration in it, inertial mass can be measured.

Q16. How can you measure gravitational mass?
W
Ans. Gravitational mass can be measured by the relation, m = . Here W is the weight of the body and
g is acceleration due to gravity at that place. g
Q17. What is the relation between inertial mass and gravitational mass of a body?
Ans. The two masses are found to be equal.

Q18. Which instrument determines the inertial mass?
Ans. An inertial balance determines the inertial mass.

Q19. Which instrument determines the gravitational mass?
Ans. A spring balance and a physical balance determines the gravitational mass.

Q20. What is the principle of a physical balance?
Ans. It works on the principle of moment.

Q21. Is balance a lever?
Ans. Yes, it is a lever of fi rst kind since fulcrum is always between eff orts and load.

Q22. What is the function of the screws S and S at the end of the beam?
2
1
Ans. These screws S and S are used to make the beam horizontal.
1
2
Q23. Of which substance are the knife edges made of and why?
Ans. Agate. It is a very hard substance and does not wear and tear easily.

Q24. Why is it necessary to close the shutters of the glass case for an accurate measurement?
(NCERT)
Ans. For an accurate measurement, it is necessary to close the shutters of the glass case because air may
enter the weighing box which may aff ect the accurate measurement of the substance.

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