Three equal weights of 3 kg each are hanging on a string passing over a frictionless pulley as shown in figure. The tension in the string between masses  II  and  III  will be ( Take  g = 10 m/sec² )

• 5 N

• 6 N

• 10 N

• 20 N

Assertion:  Impulsive  force  is  large  and  acts  for a short time.

Reason: Finite  change  in  momentum  should  be  produced  by  the  force.

• If both assertion and reason are true and reason is the correct explanation of assertion

• If both assertion and reason are true but reason is not the correct explanation of assertion

• If assertion is true but reason is false

• If both assertion and reason are false

Side of an equilateral triangle is l. Three point masses each of magnitude m, are placed at the three vertices of the triangle. Moment of inertia of this system about one side of the triangle as axis is given by

• $\frac{3\mathrm{m} {\mathrm{l}}^2}{4}$

• $\frac{4}{3}{\mathrm{ml}}^2$

• $\frac{3}{2}{\mathrm{ml}}^2$

• $\frac{2}{3}{\mathrm{ml}}^2$

In the diagram shown below all three rods are of equal length Land equal mass M. The system is rotated such that rod B is the axis. What is the moment of inertia of the system?

• $\frac{{\mathrm{ML}}^2}{6}$

• $\frac{4}{3}$ML²

• $\frac{{\mathrm{ML}}^2}{3}$

• $\frac{2}{3} {\mathrm{ML}}^2$

The direction of the angular velocity vector is along

• the tangent to the circular path

• the inward radius

• the outward radius

• the axis of rotation

A man of mass 60 kg records his wt on a weighing machine placed inside a lift. The ratio of wts. of  man recorded when lift is ascending up with a uniform speed of 2 m/s to when it is descending down with a uniform speed of 4 m/s will be

• 0.5

• 1

• 2

• none of these

The moment of inertia of a rod about an axis through its centre and perpendicular to it is $\frac{1}{12}$ ML² ( where M is the mass and L, the length of the rod). The rod is bent in the middle so that the two halves make an angle of 60^°. The moment of inertia of the bent rod about the same axis would be

• $\frac{1}{48}$ ML²

• $\frac{1}{12}$ML²

• $\frac{1}{24}$ ML²

• $\frac{{\mathrm{ML}}^2}{8\sqrt{3}}$

Assertion:  A judo fighter in order to throw his opponent on to the mat tries to initially bend his opponent and then rotate him around his hip. 

Reason: As the mass of the opponent is brought closer to the fighter's hip, the force required to throw the opponent is reduced.

• If both assertion and reason are true and reason is the correct explanation of the assertion

• If both assertion and reason are true but reason is not the correct explanation of the assertion

• If assertion is true, but reason is false

• Both assertion and reason are false statements

189.

In the figure, the position-time graph of a particle of mass 0.1 kg is shown. The impulse at t = 2 sec is

  

• 0.2 kg m sec^-1

• - 0.2 kg m sec^-1

• 0.1 kg m sec^-1

• - 0.4 kg m sec^-1

The pressure exerted by an electromagnetic wave of intensity I ( watt/m² ) on a nonreflecting surface is [ c is the velocity of light ]

• Ic

• Ic²

• I/c

• I/c²