# VECTORS

1. If a vector making angles α, β, and γ respectively with the X, Y and Z axes respectively. Then sin2α + sin2β+ sin2γ =
Ans: 2
Explanation:

2. If the resultant of n forces of different magnitudes acting at a point is zero, then the minimum value of n is
Ans: 3
Explanation: If vectors are of equal magnitude then two vectors can give zero resultant, if they works in opposite direction. But if the vectors are of different magnitudes then minimum three vectors are required to give zero resultant.

3. Can the resultant of 2 vectors be zero
Ans: Yes, when the 2 vectors are same in magnitude but opposite in sense

4. The sum of the magnitudes of two forces acting at point is 18 and the magnitude of their resultant is 12. If the resultant is at 90o with the force of smaller magnitude, what are the, magnitudes of forces
Ans: 5, 13
Explanation: Let P be the smaller force and Q be the greater force then according to problem –

5. A vector  is turned without a change in its length through a small angle dθ. The value of   and Δa are respectively
Ans: a dθ, O

Explanation:

6. Find the resultant of three vectors   and  shown in the following figure. Radius of the circle is R.

Ans:
Explanation:

7. Figure shows ABCDEF as a regular hexagon. What is the value of
Ans:

8. The length of second's hand in watch is 1 cm. The change in velocity of its tip in 15 seconds is
Ans:
Explanation:

9. A particle moves towards east with velocity 5 m/s. After 10 seconds its direction changes towards north with same velocity. The average acceleration of the particle is
Ans:
Explanation:

10. A force   (where K is a positive constant) acts on a particle moving in the x-y plane. Starting from the origin, the particle is taken along the positive x- axis to the point (a, 0) and then parallel to the y-axis to the point (a, a). The total work done by the forces  on the particle is
Ans: − Ka2
Explanation:

11. The vectors from origin to the points A and B are   and   respectively. The area of the triangle OAB be
Ans:    sq.unit
Explanation:

12. A metal sphere is hung by a string fixed to a wall. The sphere is pushed away from the wall by a stick. The forces acting on the sphere are shown in the second diagram. Which of the following statements is wrong
Ans:  T = P + W

Explanation:

13. The speed of a boat is 5 km/h in still water. It crosses a river of width 1 km along the shortest possible path in 15 minutes. The velocity of the river water is
Ans:  3 km/h

14. A man crosses a 320 m wide river perpendicular to the current in 4 minutes. If in still water he can swim with a speed 5/3 times that of the current, then the speed of the current, in m/min is
Ans:  60

15.   represents a unit vector when c is
Ans:
Explanation:

16. The angles which a vector  makes with X, Y and Z axes respectively are
Ans: 60o, 60o, 45o
Explanation:

17. The value of a unit vector in the direction of vector
Ans:

Explanation:

18. Which of the following is independent of the choice of coordinate system
Ans:

19. A car travels 6 km towards north at an angle of 45° to the east and then travels distance of 4 km towards north at an angle of 135° to the east. How far is the point from the starting point. What angle does the straight line joining its initial and final position makes with the east
Ans: : and tan−1(5)
Explanation:

20. Given that  out of three vectors two are equal in magnitude and the magnitude of third vector is  times that of either of the two having equal magnitude. Then the angles between vectors are given by
Ans: 90°, 135°, 135°

From polygon law, three vectors having summation zero should form a closed polygon. (Triangle) since the two vectors are having same magnitude and the third vector is  times that of either of two having equal magnitude. i.e. the triangle should be right angled triangle
Angle between A and B, α = 90o
Angle between B and C, β = 135o
Angle between A and C, γ = 135o

21. Two forces F1 = 1 N and F2 = 2 N act along the lines x = 0 and y = 0 respectively. Then the resultant of forces would be
Ans:

Explanation:

22. At what angle must the two forces (x + y) and (x – y) act so that the resultant may be
Ans:
Explanation:

23. Following forces start acting on a particle at rest at the origin of the co-ordinate system simultaneously

and  then the particle will move

Ans: In y – z plane
Explanation:

24. The resultant of   is  On reversing the vector  the resultant becomes

What is the value of
Ans: 2(A2 + B2)
Explanation:

25. Figure below shows a body of mass M moving with the uniform speed on a circular path of radius, R. What is the change in acceleration in going from P1 to P2
Ans:

Explanation:

26. A particle is moving on a circular path of radius r with uniform velocity v. The change in velocity when the particle moves from P to Q is
Ans: 2v sin 40°
Explanation:

27.   and   are two vectors. The angle between them will be
Ans: 60°
Explanation:

28.  and  then projection of   on  will be
Ans:

Explanation:

29. In above example a unit vector perpendicular to both

and  will be
(a)           (b)        (c) Both (a) and (b)         (d) None of these
Ans: Both (a) and (b)
Explanation:

30. Two constant forces  (N) and  (N) act on a body and displace it from the position

(m) to the position  (m). What is the work done
Ans:  9 J
Explanation:

31. For any two vectors  and , if  the magnitude of  equal to
Ans:
Explanation:

32. Which of the following is the unit vector perpendicular to  and

Ans:

Explanation:

33. Two vectors  and    will be parallel if
Ans:  b = 2
Explanation:

34. Which of the following is not true ? If  and  where A and B are the magnitudes of   and
Ans:
Explanation:

35. The area of the triangle formed by  is
Ans:

Explanation:

36. Two trains along the same straight rails moving with constant speed 60 km/hr and 30 km/hr respectively towards each other. If at time t = 0 , the distance between them is 90 km, the time when they collide is
Ans:  1 hr
Explanation:

37. A steam boat goes across a lake and comes back (a) On a quite day when the water is still and (b) On a rough day when there is uniform air current so as to help the journey onward and to impede the journey back. If the speed of the launch on both days was same, in which case it will complete the journey in lesser time
Ans: Case (b)
Explanation:

38. To a person, going eastward in a car with a velocity of 25 km/hr, a train appears to move towards north with a velocity of   km/hr. The actual velocity of the train will be
Ans: 25 km/hr
Explanation:

39. A swimmer can swim in still water with speed υ and the river is flowing with velocity v/2. To cross the river in shortest distance, he should swim making angle θ with the upstream. What is the ratio of the time taken to swim across the shortest time to that is swimming across over shortest distance
Ans: sin θ

40. A bus is moving with a velocity 10 m/s on a straight road. A scooterist wishes to overtake the bus in 100 s. If the bus is at a distance of 1 km from the scooterist, with what velocity should the scooterist chase the bus
Ans: 20 m/s
Explanation:

Assertion Reason

Read the assertion and reason carefully to mark the correct option out of the options given below:
(a) If both assertion and reason are true and the reason is the correct explanation of the assertion.
(b) If both assertion and reason are true but reason is not the correct explanation of the assertion.
(c) If assertion is true but reason is false.
(d) If the assertion and reason both are false.
(e) If assertion is false but reason is true.

Reason :   as well as   lie in the plane containing  and , but

lies perpendicular to the plane containing  and .
Ans: Both assertion and reason are true and the reason is the correct explanation of the assertion.
Explanation: Cross product of two vectors is perpendicular to the plane containing both the vectors.

2. Assertion :
Reason :  is equally inclined to both  and  and the angle between  and

is 90°
Ans: Both assertion and reason are true and the reason is the correct explanation of the assertion.
Explanation:

Reason :  is perpendicular to .

Ans: The assertion and reason both are false.
Explanation:

4. Assertion :
Reason :
Ans: Both assertion and reason are true but reason is not the correct explanation of the assertion.
Explanation:

5. Assertion : Vector product of two vectors is an axial vector
Reason : If   = instantaneous velocity,  = radius vector and

= angular velocity, then
Ans: Assertion is true but reason is false.
Explanation:

6. Assertion : Minimum number of non-equal vectors in a plane required to give zero resultant is three.
Reason : If ,  then they must lie in one plane
Ans: Both assertion and reason are true but reason is not the correct explanation of the assertion.
Explanation: For giving a zero resultant, it should be possible to represent the given vectors along the sides of a closed polygon and minimum number of sides of a polygon is three.

7. Assertion : Relative velocity of A w.r.t. B is greater than the velocity of either, when they are moving in opposite directions.
Reason : Relative velocity of A w.r.t.

Ans: Both assertion and reason are true and the reason is the correct explanation of the assertion.
Explanation:

8. Assertion : Vector addition of two vectors A and B is commutative.
Reason :
Ans: Both assertion and reason are true but reason is not the correct explanation of the assertion.
Explanation:

9. Assertion :
Reason : Dot product of two vectors is commutative.
Ans: Both assertion and reason are true and the reason is the correct explanation of the assertion.

10. Assertion :
Reason : Cross product of vectors is commutative.

Ans: Assertion is true but reason is false.
Explanation:

11. Assertion : A negative acceleration of a body is associated with a slowing down of a body.
Reason : Acceleration is vector quantity.
Ans: Both assertion and reason are true but reason is not the correct explanation of the assertion.

12. Assertion : A physical quantity cannot be called as a vector if its magnitude is zero.
Reason : A vector has both, magnitude and direction.
Ans: Assertion is false but reason is true.
Explanation: If a vector quantity has zero magnitude then it is called a null vector. That quantity may have some direction even if its magnitude is zero.

13. Assertion : The sum of two vectors can be zero.
Reason : The vector cancel each other, when they are equal and opposite.
Ans: Both assertion and reason are true and the reason is the correct explanation of the assertion.

Explanation:

14. Assertion : Two vectors are said to be like vectors if they have same direction but different magnitude.
Reason : Vector quantities do not have specific direction.
Ans: If assertion is true but reason is false.
Explanation: If two vectors are in opposite direction, then they cannot be like vectors.

15. Assertion : The scalar product of two vectors can be zero.
Reason : If two vectors are perpendicular to each other, their scalar product will be zero.
Ans: If both assertion and reason are true and the reason is the correct explanation of the assertion.
Explanation:

16. Assertion : Multiplying any vector by an scalar is a meaningful operations.
Reason : In uniform motion speed remains constant.
Ans: Both assertion and reason are true but reason is not the correct explanation of the assertion.
Explanation:  We can multiply any vector by any scalar. For example, in equation  mass is a scalar quantity, but acceleration is a vector quantity.

17. Assertion : A null vector is a vector whose magnitude is zero and direction is arbitrary.
Reason : A null vector does not exist.
Ans: Assertion is true but reason is false.
Explanation:  If two vectors equal in magnitude are in opposite direction, then their sum will be a null vector. A null vector has direction which is intermediate (or depends on direction of initial vectors) even its magnitude is zero.

18. Assertion : If dot product and cross product of  and  are zero, it implies that one of the vector  and  must be a null vector.
Reason : Null vector is a vector with zero magnitude.
Ans: Both assertion and reason are true but reason is not the correct explanation of the assertion.

Explanation:

If  and

are not null vectors then it follows that sin θ and cos θ both should be zero simultaneously. But it cannot be possible so it is essential that one of the vector must be null vector.

19. Assertion : The cross product of a vector with itself is a null vector. A
Reason : The cross-product of two vectors results in a vector quantity.
Ans: Both assertion and reason are true but reason is not the correct explanation of the assertion.

20. Assertion : The minimum number of non coplanar vectors whose sum can be zero, is four.
Reason : The resultant of two vectors of unequal magnitude can be zero.
Ans:  Assertion is true but reason is false.
Explanation:  The resultant of two vectors of unequal magnitude given by   cannot be zero for any value of θ.

21. Assertion :
Reason : The dot product of two vectors involves cosine of the angle between the two  vectors.
Ans: Both assertion and reason are true and the reason is the correct explanation of the assertion.
Explanation:

22. Assertion :  Vector addition is commutative.
Reason :
Ans: Assertion is true but reason is false.
Explanation:

Posted Date : 19-02-2021

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గమనిక : ప్రతిభ.ఈనాడు.నెట్‌లో కనిపించే వ్యాపార ప్రకటనలు వివిధ దేశాల్లోని వ్యాపారులు, సంస్థల నుంచి వస్తాయి. మరి కొన్ని ప్రకటనలు పాఠకుల అభిరుచి మేరకు కృత్రిమ మేధస్సు సాంకేతికత సాయంతో ప్రదర్శితమవుతుంటాయి. ఆ ప్రకటనల్లోని ఉత్పత్తులను లేదా సేవలను పాఠకులు స్వయంగా విచారించుకొని, జాగ్రత్తగా పరిశీలించి కొనుక్కోవాలి లేదా వినియోగించుకోవాలి. వాటి నాణ్యత లేదా లోపాలతో ఈనాడు యాజమాన్యానికి ఎలాంటి సంబంధం లేదు. ఈ విషయంలో ఉత్తర ప్రత్యుత్తరాలకు, ఈ-మెయిల్స్ కి, ఇంకా ఇతర రూపాల్లో సమాచార మార్పిడికి తావు లేదు. ఫిర్యాదులు స్వీకరించడం కుదరదు. పాఠకులు గమనించి, సహకరించాలని మనవి.