11.

Two blocks of masses 2 kg and 4 kg are attached by an inextensible light string as shown in the figure. If a force of 120 N pulls the blocks vertically upward, the tension in the string is (take g = 10 ms^-2)

              

• 20 N

• 15 N

• 35 N

• 40 N

The total energy of a solid sphere of mass 300 g which rolls without slipping with a constant velocity of 5 ms^-1 along a straight line is

• 5.25 J

• 3.25 J

• 0.25 J

• 1.25 J

A bullet when fired into a target loses half of its velocity after penetrating 20 cm. Further distance of penetration before it comes to rest is

• 6.66 cm

• 3.33 cm

• 12.5 cm

• 10 cm

In elastic collision

• both momentum and kinetic energy are conserved

• neither momentum nor kinetic energy is conserved

• only momentum is conserved

• only kinetic energy is conserved

Two discs rotating about their respective axis of rotation with angular speed 2 rad s^-1 and 5 rad s^-1 are brought into contact such that their axes of rotation coincide. Now, the angular speed of the system becomes 4 rads^-1 . If the moment of inertia of the second disc is 1 x 10^-3 kg m² then the moment of inertia of the first disc (in kg m²) is

• 0.25 × 10^-3

• 1.5 × 10^-3

• 0.5 × 10^-3

• 0.75 × 10^-3

A wheel is rotating at 1800 rpm about its own axis. When the power is switched off, it comes to rest in 2 min. Then, the angular retardation in rads^-1 is

• $2\mathrm{\pi }$

• $\mathrm{\pi }$

• $\mathrm{\pi }/2$

• $\mathrm{\pi }/4$

If the angular momentum· of a particle of mass m rotating along a circular path of radius r with uniform speed is L, the centripetal force acting on the particle is

• $\frac{{\mathrm{L}}^2}{{\mathrm{mr}}^3}$

• $\frac{{\mathrm{L}}^2}{\mathrm{mr}}$

• $\frac{\mathrm{L}}{{\mathrm{mr}}^2}$

• $\frac{{\mathrm{L}}^2\mathrm{m}}{\mathrm{r}}$

Pick out the wrong statement from the following

• The SI unit of universal gravitational constant is Nm²kg^-2

• The gravitational force is a conservative force

• $\mathrm{Gravitational} \mathrm{potential} \mathrm{energy} = \frac{\mathrm{gravitational} \mathrm{potential}}{\mathrm{mass} \mathrm{of} \mathrm{the} \mathrm{body}}$

• The centripetal acceleration of the satellite is equal to acceleration due to gravity

If a body of mass m has to be taken from the surface to the earth to a height h = R, then the amount of energy required is (R = radius of the earth)

• mgR

• $\frac{\mathrm{mgR}}{3}$

• $\frac{\mathrm{mgR}}{2}$

• $\frac{\mathrm{mgR}}{12}$

The total energy of an artificial satellite of mass m revolving in a circular orbit around the earth with a speed v is

• $\frac{1}{2} {\mathrm{mv}}^2$

• $\frac{1}{4} {\mathrm{mv}}^2$

• $- \frac{1}{2} {\mathrm{mv}}^2$

• − mv²