Work And Energy MCQs | Physics MCQs

The formula for escape velocity is v_e = √(2GM/R). It depends on the mass (M) and radius (R) of the planet, but not on the mass of the escaping object.

In an ideal system without air resistance, the total mechanical energy (sum of kinetic and potential energy) of a simple pendulum is conserved.

Since 1 horsepower (hp) is approximately 746 Watts, 2238 W / 746 W/hp = 3 hp.

Using the relationship KE = p²/(2m), if the momentum 'p' is doubled, the kinetic energy becomes (2p)²/(2m) = 4p²/(2m), which is four times the original KE.

Friction always acts in the direction opposite to motion. Since the angle between the frictional force and displacement is 180°, the work done by friction is always negative.

Using the relationship p = √(2mKE), if KE is constant, momentum 'p' is proportional to the square root of mass (√m). Therefore, the heavier body has greater momentum.

A Kilowatt (kW) is a unit of power (1000 Joules per second). A Kilowatt-hour (kWh) is a unit of energy (Power × time).

The work done by a conservative force is equal to the negative change in potential energy (W_c = -ΔPE). If W_c is positive, ΔPE must be negative, meaning the potential energy decreases.

Power can be calculated as P = F × v. Therefore, P = 500 N × 20 m/s = 10,000 Watts or 10 kW.

By the law of conservation of energy, the initial potential energy (mgh) is completely converted into kinetic energy just before impact (assuming h=0 is the ground).

The acceleration due to gravity 'g' on the Moon is about 1/6th of that on Earth. Since work against gravity is W=mgh, less work is required on the Moon.

Non-conservative forces like friction or air resistance do work that dissipates mechanical energy, usually as heat, thus changing the total KE + PE of the system.

The stored potential energy is PE = ½kx². If 'k' is doubled while 'x' remains the same, the stored energy will also be doubled.

From KE = ½mv², to have the same KE, the object with the smaller mass (the car) must have a higher velocity.

Both the satellite and the object inside are constantly falling towards the Earth due to gravity, but they also have a high tangential velocity that keeps them in orbit. This state of continuous free fall creates the sensation of weightlessness.

The velocity required to maintain a stable low-Earth orbit is approximately 7.9 km/s. This is less than the escape velocity.

The formula for instantaneous power is P = Fv, assuming the force and velocity are in the same direction.

The Sun generates energy through nuclear fusion, where hydrogen nuclei combine under immense temperature and pressure to form helium, releasing a tremendous amount of energy in the process.

First, calculate the work done (potential energy gain): W = mgh = 200*10*20 = 40,000 J. Then, calculate power: P = W/t = 40,000 J / 10 s = 4000 W or 4 kW.

Solar cells (photovoltaic cells) are designed to directly convert sunlight (light energy) into electrical energy through the photovoltaic effect.

Work is defined as force multiplied by displacement (W=Fd). If the displacement is zero, the work done is zero, regardless of the magnitude of the force.

The force (friction) is opposed to the motion, so the angle is 180°. W = Fd cos(180°) = 200 N * 10 m * (-1) = -2000 J.

Einstein's famous equation, E=mc², states that energy (E) and mass (m) are equivalent and can be converted into one another, with c² being the conversion factor.

For any gravitationally bound system, like a satellite in orbit, the total mechanical energy (KE + PE) is negative. A positive or zero total energy would mean the object is not in a bound orbit and can escape.

Escape velocity v_e = √(2GM/R). Since 'v' is inversely proportional to the square root of 'R', halving 'R' to R/2 will multiply the velocity by √2.

To find the work done by a variable force, we calculate the area under the Force-Displacement graph by dividing it into a large number of small rectangular intervals and summing their areas.

Since there is no displacement of the wall, the work done on the wall is zero, according to the physics definition of work (W=Fd).

As the body falls, its potential energy is converted into kinetic energy. In the absence of air resistance, the total mechanical energy (PE + KE) remains constant.

Given ½m₁v₁² = ½m₂v₂², we can rearrange to get v₁²/v₂² = m₂/m₁. Taking the square root gives v₁/v₂ = √(m₂/m₁).

Stretching or compressing an elastic object, like a rubber band or a spring, stores energy in it in the form of elastic potential energy.

While degrees are commonly used, the standard SI unit for angular displacement, which is necessary for rotational motion equations, is the radian.

A full circle (360°) corresponds to an arc length equal to its circumference (2πr). Since θ = s/r, one revolution is θ = (2πr)/r = 2π radians.

Angular velocity (ω) is defined as the rate at which the angular displacement (θ) changes with respect to time (ω = Δθ/Δt).

The tangential linear velocity of a point on a rotating object is given by the product of its distance from the axis (radius) and its angular velocity.

Using the right-hand rule, if you curl the fingers of your right hand in the direction of rotation, your thumb points in the direction of the angular velocity vector.

Centripetal acceleration (a_c) is the acceleration that causes an object to change its direction to follow a circular path, and it is always directed towards the center of the circle.

Centripetal acceleration can be expressed as a_c = v²/r or, by substituting v=rω, as a_c = rω².

Centripetal force is the net force that produces centripetal acceleration. It is not a fundamental force but the net result of other forces (like tension, gravity, or friction).

Since F = ma, the centripetal force is F_c = ma_c. Substituting a_c = v²/r gives F_c = mv²/r.

Moment of inertia (I) is a measure of an object's resistance to changes in its rotational motion, just as mass is a measure of resistance to changes in linear motion.

Moment of inertia (I) is determined by the total mass of the object and how that mass is geometrically distributed relative to the axis of rotation (I = Σmr²).

Torque (τ) is the rotational equivalent of linear force; it is a twisting force that causes an object to undergo angular acceleration.

Just as F=ma relates force, mass, and linear acceleration, τ = Iα relates torque (τ), moment of inertia (I), and angular acceleration (α).

Angular momentum (L) is the rotational equivalent of linear momentum and is calculated as the product of the moment of inertia and angular velocity.

Similar to linear momentum, the total angular momentum of an isolated system (one with zero net external torque) is conserved.

By pulling her limbs in, the diver decreases her moment of inertia (I). To conserve angular momentum (L = Iω), her angular velocity (ω) must increase.

The kinetic energy due to rotation is given by K.E_rot = ½Iω², which is analogous to the linear kinetic energy formula K.E = ½mv².

A rolling object is both moving from one place to another (translation) and spinning (rotation), so its total kinetic energy is the sum of both forms.

The solid sphere has a smaller moment of inertia than the hollow sphere. This means less of its potential energy is converted to rotational KE and more to translational KE, making it faster.

The specific speed required to maintain a stable orbit at a certain altitude is called orbital velocity. For low-Earth orbit, this is about 7.9 km/s.

A geostationary satellite orbits above the equator with an orbital period of exactly 24 hours, causing it to appear stationary from the ground.

Objects in orbit are continuously falling towards the central body but have enough tangential velocity to miss it. This state of constant free-fall results in the feeling of weightlessness.

By spinning a ring-shaped space station, the normal force exerted by the inner floor on an astronaut provides the necessary centripetal force, simulating the sensation of gravity.

The simulated gravity is the centripetal acceleration (a_c = rω²). To achieve a_c = g, the required angular velocity (ω), and thus frequency, depends on the radius 'r' of the station.

The apparent weight (normal force) is N = m(g-a). When accelerating down, the apparent weight is less than the true weight.

On a banked road, the road is tilted. The normal force is perpendicular to the road surface, and its horizontal component points towards the center of the curve, providing the centripetal force.

A flywheel has a large moment of inertia and is used to store rotational kinetic energy, resisting changes in speed and ensuring smoother operation.

Angular acceleration (α) is the rate of change of angular velocity, so its unit is radians per second per second, or rad/s².

Angular acceleration α = Δω/Δt = (10 - 2) rad/s / 4 s = 8/4 = 2 rad/s².

While centripetal acceleration changes the direction, tangential acceleration (a_t = rα) acts along the tangent to the path and is responsible for changing the object's speed.

In uniform circular motion, the magnitude of the velocity (speed) is constant, but the direction of the velocity vector is continuously changing, resulting in a non-zero centripetal acceleration.

For a thin hoop or ring, all the mass (M) is located at the same distance (R) from the axis of rotation, so its moment of inertia is I = MR².

Centrifugal force is an apparent outward force experienced by an object in a rotating frame of reference. It is not a real force but rather the effect of the object's inertia.

The moment of inertia is largest when the mass is distributed farthest from the axis of rotation. In a thin hoop, all the mass is at the maximum radius R.

A geostationary satellite remains above the same point on Earth because its orbital period is exactly the same as Earth's rotational period (24 hours).

The static friction between the tires and the road surface provides the necessary inward force to make the car change direction and follow the curve.

Angular momentum is L = r x p. If the particle's path passes through the origin (the reference point), the position vector 'r' is always parallel to the momentum vector 'p', making their cross product zero.

Angular momentum L = Iω. The unit for I is kg m² and for ω is rad/s (or s⁻¹). Therefore, the unit for L is kg m²/s, which is also equivalent to Joule-second (J·s).

The hollow cylinder has its mass distributed further from the central axis compared to the solid cylinder, giving it a greater resistance to rotation and thus a greater moment of inertia.

By conservation of angular momentum (L=Iω), if the Earth's radius decreases, its moment of inertia (I ≈ ⅖MR²) would decrease. To conserve L, its angular velocity (ω) would have to increase, making the day shorter.

Even at a constant speed, the direction of motion is continuously changing in a circle. Since velocity is a vector (speed + direction), the velocity is changing, which implies there is acceleration (centripetal acceleration).

Torque is calculated as the cross product of the position vector and the force vector (τ = r x F), so its unit is the Newton-meter (N·m).

Torque equals the lever arm (length of the wrench) times the force. A longer wrench increases the lever arm, allowing the same amount of force to produce a greater torque.

The law of conservation of angular momentum is the rotational equivalent of the law of conservation of linear momentum. Angular momentum is conserved when the net external torque is zero.

The gravitational force on a satellite in a circular orbit provides a torque that is zero with respect to the center of the Earth. Therefore, its angular momentum is conserved.

While we often model orbits as perfectly circular for simplicity, real-world orbits are slightly elliptical due to various perturbations and the nature of gravitational fields.

A rolling object is simultaneously translating and rotating. Its total kinetic energy is the sum of the kinetic energy of its center of mass (translational) and the kinetic energy of its rotation about the center of mass (rotational).

The formula for the moment of inertia of a single point mass is I = mr², where 'r' is the perpendicular distance from the mass to the axis of rotation.

A large moment of inertia indicates a high resistance to changes in rotational motion. This makes the object difficult to start, stop, or change its speed of rotation.

To achieve an orbital period of 24 hours, a geostationary satellite must be placed at a very specific altitude of approximately 35,786 kilometers (or about 36,000 km) above the equator.