Page 45 - Physics - XI

Q12. Do you mean that a body in equilibrium has to be necessarily at rest?
Ans. No, a body in uniform motion can also be in equilibrium. The condition for equilibrium is that there
is no net force acting on the body, i.e. there is no acceleration produced in the body.

Q13. What are rectangular components?
Ans. If a vector is resolved into components which are perpendicular to each other, these components are
called rectangular components.
Q14. Is kilogram weight a unit of force or mass?
Ans. kg wt is a unit of force.

Q15. What is the relation between kg wt and newton?
Ans. 1 kg wt = 9.8 N

Q16. How can we reduce the friction in pulleys?
Ans. By oiling the pulleys.

Q17. State parallelogram law of vector addition. (NCERT)
Ans. If two vector acting simultaneously at a point are represented both in magnitude and direction by the
adjacent sides of a parallelogram drawn from that point, then the resultant vector can be represented
both in magnitude and direction by the diagonal of the parallelogram passing through that point.

Q18. Given two forces, what could be the (NCERT)

(a) Maximum magnitude of resultant force.
(b) Minimum magnitude of resultant force.
Ans. (a) If two forces of magnitudes F and F are working in the same direction then the resultant force
1
2
will be maximum and its magnitude will be F + F .
1 2
(b) If two forces of magnitudes F and F are working in the opposite direction then the resultant
1
2
force will be minimum and its magnitude will be |F – F |.
1 2
Q19. In which situation this parallelogram can be a rhombus? (NCERT)
Ans. This parallelogram can be a rhombus if and only if the two forces are of the same magnitude.
Q20. If all the three forces are equal in magnitude, how will the parallelogram modify? (NCERT)
Ans. It is possible if the angle between any of the two forces is 120°. So, the parallelogram will be
modifi ed as
60°
120°

120°
60°

Q21. When the knot is in equilibrium position, is any force acting on the pulleys? (NCERT)
Ans. When the knot is in equilibrium position, it means that the net force acting on the knot is zero. A
force (normal reaction) acts on the pulleys.

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