The sum of the magnitudes of two forces acting at a point is 18 N

Subject

Physics

Class

JEE Class 12

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 Multiple Choice QuestionsMultiple Choice Questions

1.

The work done in moving an alpha particle between two points having potential difference 25 V is

  • 8 × 10-18 J

  • 8 × 10-19 J

  • 8 × 10-20 J

  • 8 × 10-16 J


2.

The physical quantity angular momentum has the same dimensions as that of

  • work

  • force

  • Planck's constant

  • torque


3.

The values of two resistors are R1 = (6 ± 0.3)kΩ and R2 = (10 ± 0.2)kΩ. The percentage error in the equivalent resistance when they are connected in parallel is

  • 5.125 %

  • 2 %

  • 10.125 %

  • 7 %


4.

Two trains are moving with equal speed in opposite directions along two parallel railway tracks. If the wind is blowing with speed u along the track so that the relative velocities of the trains with respect to the wind are in the ratio 1 : 2, then the speed of each train must be

  • 3u

  • 2u

  • 5u

  • 4u


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5.

Two balls are dropped to the ground from different heights. One ball is dropped 2 s after the other but they both strike the ground at the same time. If the first ball takes 5 s to reach the ground, then the difference in initial heights is (g = 10 ms-2)

  • 20 m

  • 80 m

  • 170 m

  • 40 m


6.

A ball is thrown vertically upwards with a velocity of 25 ms-1 from the top of a tower of height 30 m. How long will it travel before it hits ground ?

  • 6 s

  • 5 s

  • 4 s

  • 12 s


7.

A ball is projected from the ground at a speed of 10 ms-1 making an angle of 30° with the horizontal. Another ball is simultaneously released from a point on the vertical line along the maximum height of the projectile. The initial height of the second ball is (g = 10 ms-2)

  • 6.25 m

  • 2.5 m

  • 1.25 m

  • 5 m


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8.

The sum of the magnitudes of two forces acting at a point is 18 N and the magnitude of their resultant is 12 N. If the resultant is at 90° with the smaller force, the magnitude of the forces in N are

  • 6, 12

  • 11, 7

  • 5, 13

  • 14, 4


C.

5, 13

Let smaller force be F1. Resultant R of the forces is at 90° to AB,

∴   R2 + F12 = F22 in Δ ABC

or       (12)2 = F22 − F12                    ......... (i)

or          144 = (F2 − F1) (F2 + F1)

But,  F1 + F2 = 18 N       (given)   ....... (ii)

            

  F2 - F1 = 14418 = 8           ........ (iii)

From Eqs. (ii) and (iii),F1 = 5, F = 13
Hence, force are 5 N and 13 N.


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9.

The position of a particle is given by r = i^ + 2j^ - k^ and its linear momentum is given by p = 3i^ + 4j^ - 2k^. Then its angular momentum, about the origin is perpendicular to

  • yz-plane

  • z-axis

  • y-axis

  • x-axis


10.

A mass of 6 kg is suspended by a rope of length 2 m from a ceiling. A force of 50 N in the horizontal direction is applied at the mid-point of the rope. The angle made by the rope with the vertical, in equilibrium is

  • 50°

  • 60°

  • 30°

  • 40°


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