Two rectangular blocks A and B of masses 2 kg and 3 kg respective

Subject

Physics

Class

JEE Class 12

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 Multiple Choice QuestionsMultiple Choice Questions

1.

The number of significant figures in the numbers 4.8000 x 104 and 48000.50 are respectively

  • 5 and 6

  • 5 and 7

  • 2 and 7

  • 2 and 6


2.

A body of mass m moving along a straight line covers half the distance with a speed of 2ms-1. The remaining half of the distance is covered in two equal time intervals with a speed of 3 ms-1 and 5 ms-1 respectively. The average speed of the particle for the entire journey is

  • 38 ms-1

  • 83 ms-1

  • 43 ms-1

  • 163 ms-1


3.

The moment of inertia ofa circular ring of radius r and mass M about diameteris

  • 25 Mr2

  • Mr24

  • Mr22

  • Mr212


4.

A body of mass 0.05 kg is observed to fall with an acceleration of 9.5 ms-2. The opposing force of air on the body is (g = 9.8 ms-2)

  • 0.015 N

  • 0.15 N

  • 0.030 N

  • zero


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5.

Three concurrent co-planar forces 1 N, 2 N and 3 N acting along different directions on a body

  • can keep the body in equilibrium if 2 N and 3 N act at right angle

  • can keep the body in equilibrium if 1 N and 2 N act at right angle

  • cannot keep the body in equilibrium

  • can keep the body in equilibrium in 1 N and 3 N act at an acute angle


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6.

Two rectangular blocks A and B of masses 2 kg and 3 kg respectively are connected by a spring of spring constant 10.8 Nm-1 and are placed on a frictionless horizontal surface. The block A was given an initial velocity of 0.15 ms-1. in the direction shown in the figure. The maximum compression of the spring during the motion is

               

  • 0.01 m

  • 0.02 m

  • 0.05 m

  • 0.03 m


C.

0.05 m

As the block A moves with velocity 0.15 ms-1, it compresses the spring which pushes B towards right. A goes on compressing the spring till the velocity acquired by B becomes equal to the velocity of A, ie, 0.15 ms-1. Let this velocity be v. Now, spring is in a state of maximum compression. Let x be the maximum compression at this stage.

According to the law of conservation of linear momentum, we get

mAu = mA + mB vor  v = mAumA + mB       = 2 × 0.152 + 3 = 0.06 ms-1

According to the law of conservation of energy.

12mAu2 = 12 mA + mB v2 +12 kx212mAu2 -   12 mA + mB v2  = 12 kx212 × 2 × 0.152 - 12 2 + 3 0.062 = 12 kx20.0225 - 0.009 = 12 kx2 or 0.0135 = 12 kx2or  x = 0.027k = 0.02710.8 = 0.05 m


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7.

The work done by a force acting on a body is as shown in the graph. The total work done in covering an initial distance of 20 m is

            

  • 225 J

  • 200 J

  • 400 J

  • 175 J


8.

A door 1.6 m wide requires a force of 1 N to be applied at the free end to open or close it. The force that is required at a point 0.4 m distance from the hinges for opening or closing the door is

  • 1.2 N

  • 3.6 N

  • 2.4 N

  • 4 N


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9.

A planet revolves around the sun in an elliptical orbit. The linear speed of the planet will be maximum at

       

  • D

  • B

  • A

  • C


10.

Two sources are said to be coherent if they produce waves

  • having a constant phase difference

  • of equal wavelength

  • of equal speed

  • having same shape of wavefront


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