Science (English Medium) Class 11 - CBSE Question Bank Solutions for Physics

Figure shows (vx, t) and (vy, t) diagrams for a body of unit mass. Find the force as a function of time.

(a)

(b)

There are four forces acting at a point P produced by strings as shown in the figure, which is at rest. Find the forces F₁ and F₂.

A body is falling freely under the action of gravity alone in vacuum. Which of the following quantities remain constant during the fall?

Two inclined frictionless tracks, one gradual and the other steep meet at A from where two stones are allowed to slide down from rest, one on each track as shown in figure.

Which of the following statement is correct?

Which of the diagrams shown in figure represents variation of total mechanical energy of a pendulum oscillating in air as function of time?

A mass of 5 kg is moving along a circular path of radius 1 m. If the mass moves with 300 revolutions per minute, its kinetic energy would be ______.

In a shotput event an athlete throws the shotput of mass 10 kg with an initial speed of 1 ms^–1 at 45° from a height 1.5 m above ground. Assuming air resistance to be negligible and acceleration due to gravity to be 10 ms^–2, the kinetic energy of the shotput when it just reaches the ground will be ______.

Why is electrical power required at all when the elevator is descending? Why should there be a limit on the number of passengers in this case?

A body falls towards earth in air. Will its total mechanical energy be conserved during the fall? Justify.

A bob of mass m suspended by a light string of length L is whirled into a vertical circle as shown in figure. What will be the trajectory of the particle if the string is cut at

1. Point B?
2. Point C? 
3. Point X?

A baloon filled with helium rises against gravity increasing its potential energy. The speed of the baloon also increases as it rises. How do you reconcile this with the law of conservation of mechanical energy? You can neglect viscous drag of air and assume that density of air is constant.

A particle of mass m is moving in yz-plane with a uniform velocity v with its trajectory running parallel to + ve y-axis and intersecting z-axis at z = a (Figure). The change in its angular momentum about the origin as it bounces elastically from a wall at y = constant is ______.

A Merry-go-round, made of a ring-like platform of radius R and mass M, is revolving with angular speed ω. A person of mass M is standing on it. At one instant, the person jumps off the round, radially away from the centre of the round (as seen from the round). The speed of the round afterwards is ______.

Choose the correct alternatives:

1. For a general rotational motion, angular momentum L and angular velocity ω need not be parallel.
2. For a rotational motion about a fixed axis, angular momentum L and angular velocity ω are always parallel.
3. For a general translational motion , momentum p and velocity v are always parallel.
4. For a general translational motion, acceleration a and velocity v are always parallel.

Figure shows two identical particles 1 and 2, each of mass m, moving in opposite directions with same speed v along parallel lines. At a particular instant, r₁ and r₂ are their respective position vectors drawn from point A which is in the plane of the parallel lines. Choose the correct options:

1. Angular momentum l₁ of particle 1 about A is l₁ = mvd₁
2. Angular momentum l₂ of particle 2 about A is l₂ = mvr₂
3. Total angular momentum of the system about A is l = mv(r₁ + r₂)
4. Total angular momentum of the system about A is l = mv (d₂ − d₁)

⊗ represents a unit vector coming out of the page.

⊗ represents a unit vector going into the page.

The net external torque on a system of particles about an axis is zero. Which of the following are compatible with it?

1. The forces may be acting radially from a point on the axis.
2. The forces may be acting on the axis of rotation.
3. The forces may be acting parallel to the axis of rotation.
4. The torque caused by some forces may be equal and opposite to that caused by other forces.

A uniform cube of mass m and side a is placed on a frictionless horizontal surface. A vertical force F is applied to the edge as shown in figure. Match the following (most appropriate choice):

A uniform sphere of mass m and radius R is placed on a rough horizontal surface (Figure). The sphere is struck horizontally at a height h from the floor. Match the following:

A door is hinged at one end and is free to rotate about a vertical axis (Figure). Does its weight cause any torque about this axis? Give reason for your answer.

Two discs of moments of inertia I₁ and I₂ about their respective axes (normal to the disc and passing through the centre), and rotating with angular speed ω₂ and ω₂ are brought into contact face to face with their axes of rotation coincident.

1. Does the law of conservation of angular momentum apply to the situation? why?
2. Find the angular speed of the two-disc system.
3. Calculate the loss in kinetic energy of the system in the process.
4. Account for this loss.