Physics – Class 11 Practice Test 5

1. A ring of radius 7cm is rotating about the central axis perpendicular to its plane. A force acts on it, tangentially, such that it does a work of 10J in a complete rotation. Find the value of that force. `

500/7π N

0.7 N

0.5/7π N

35π N

2. Consider a hollow cubical box of uniform density half-filled with water and the other half filled with air as shown in the figure. Which of the marked points are the likely positions of the centre of mass of the system?

3. A rod is rotating about one end. If a force F₁ acting on the other end produces a torque T & supplies power P, find the value of force F₂ that will produce the same amount of power when it acts at the midpoint of the rod. Assume that all forces are perpendicular to the axis of rotation & axis of rod. The rod starts from rest.

= F₁

No force acting at any other point will produce the same power

> F₁

< F₁

4. Two bodies of masses 5 kg and 3 kg are moving towards each other at velocities of 3 m/s and 5 m/s, respectively. What is the velocity of their centre of mass?

0.5 m/s towards 5 kg

The centre of mass is stationary

0.25 m/s towards 3 kg

Upredictable

5. An asteroid enters the atmosphere of the earth and breaks into two pieces. One of the pieces is larger than the other. Which of the following is true considering the centre of mass of both the pieces together?

The centre of mass remains in the same trajectory as before breaking apart of the asteroid

The centre of mass shifts horizontally towards the larger piece

The centre of mass shifts horizontally towards the smaller piece

Depends on the velocity of the asteroid

6. The moment of inertia of a planar square about a planar axis parallel to one side is 10kgm². What is the moment of inertia about a diagonal?

20kgm²

10kgm²

5kgm²

1kgm²

7. The angular momentum vector of a particle about a point on the rotational axis is parallel to its angular velocity vector, provided the particle rotates with fixed speed about that axis. True or False?

True

False

8. Three objects of mass 1 kg each are placed at corners of a right-angled triangle AOB as shown in the figure. Consider ‘O’ as the origin and OA = OB = 1m. Determine the position of the centre of mass of this system.

(i- j) m

1/3 (i+ j) m

2/3 (i + j) m

1/3 (i- j) m

9. A ball of mass 2kg is moving with a speed of 10m/s along a flat surface. It collides with another ball of mass 3kg and comes to rest, what will be the speed of the second ball after collision?

6.67m/s

Zero

20m/s

The above said situation is not possible

10. The angular speed of a body is 2rpm. What should be the angular acceleration for the angular speed to double up in 5s?

-2π/75 rad/s²

π/75 rad/s²

-π/75 rad/s²

2π/75 rad/s²