11.

Which one of the following is not a contact force ?

• Viscous force

• Air resistance

• Magnetic force

• Buoyant force

A force $\left(4\hat{\mathrm{i}} + \hat{\mathrm{j}} - 2\hat{\mathrm{k}}\right)$ N acting on a body maintains its velocity at $\left(2\hat{\mathrm{i}} + 2\hat{\mathrm{j}} + 3\hat{\mathrm{k}}\right)$ ms^-1. The power exerted is

• 4 W

• 5 W

• 2 W

• 8 W

Energy required to break one bond in DNA is

• 10^-10 J

• 10^-18 J

• 10^-7 J

• 10^-20 J

Identify the false' statement from the following

• Work-energy theorem is not independent of Newton's second law

• Work-energy theorem holds in all inertial frames

• Work done by friction over a closed path is zero

• No potential energy can be associated with friction

Three bricks each of length L and mass M are arranged as shown from the wall. The distance of the centre of mass of the system from the wall is

• L/4

• L/2

• (3/2)L

• (11/12)L

A fly wheel of moment of inertia 3 x 10² kg m² is rotating with uniform angular speed of 4.6 rads^-1. If a torque of 6.9 x 10² Nm retards the wheel, then the time in which the  wheel comes to rest is

• 1.5 s

• 2 s

• 0.5 s

• 1 s

Moment of inertia of a ring of mass M and radius R about a tangent to the circle of the ring is

• $\frac{5}{2} {\mathrm{MR}}^2$

• $\frac{3}{2} {\mathrm{MR}}^2$

• $\frac{1}{2} {\mathrm{MR}}^2$

• MR²

If the escape velocity of a planet is 3 times that of the earth and its radius is 4 times that of the earth, then the mass of the planet is (Mass of the earth = 6 x 10²⁴ kg)

• 1.62 × 10²² Kg

• 0.72 × 10²² kg

• 2.16 × 10²⁶ kg

• 1.22 × 10²² kg

The total energy of a circularly orbiting satellite is

• twice the kinetic energy of the satellite

• half the kinetic energy of the satellite

• half the potential energy of the satellite

• equal to the potential energy of the satellite

If an earth satellite of mass m orbiting at a distance 2R from the centre of earth has to be transferred into the orbit of radius 3 R, the amount of energy required is (R = radius of earth)

• mgR

• $\frac{\mathrm{mgR}}{3}$

• $\frac{\mathrm{mgR}}{2}$

• $\frac{\mathrm{mgR}}{12}$