Physics Mechanics

Explanation

Ball bearings are utilized in bicycles, cars, and other machinery to minimize friction. Friction is related to the effective surface area, so reducing the effective surface area can decrease friction. This is why ball bearings are preferred for their ability to lower friction by reducing the effective area of contact between the wheel and axle.

Explanation

An artificial satellite remains in orbit around the Earth without falling due to the Earth's gravitational pull providing the necessary acceleration for its motion. This acceleration is constant in magnitude but changes in direction as the satellite moves in a circular orbit.

Explanation

When the same material and load are applied to four wires with varying dimensions, the wire that will elongate the most is the one with a length of 3m and a diameter of 1.5mm. This is because the elongation in a wire is directly proportional to its length and inversely proportional to the square of its radius. Therefore, the wire with dimensions of 3m length and 1.5mm diameter will experience the maximum extension when subjected to the same load.

Explanation

In this physics scenario, vessels A, B, and C are filled with water, mercury, and kerosene to the same level, and each has a tap at the bottom. When all taps are opened together, vessel C, containing kerosene with the lowest viscosity, will be emptied first.

Explanation

The average speed at which the Earth orbits the sun is approximately 30 kilometers per second.

Explanation

In descending order of density, the correct sequence of the substances is Gold > Mercury > Steel. This is because gold has a density of 19.30 g/cm³, mercury has a density of 13.534 g/cm³, and steel has a density of 7.80 g/cm³.

Explanation

In this scenario, a car is moving at a steady pace of 60 km/h on a road. When a vehicle travels at a constant speed, there is no acceleration (a=0). According to Newton's second law, F=ma. Therefore, if acceleration is zero, the net resultant force acting on the car is also zero.

Explanation

When a spherical object travels in a circular path with a consistent angular velocity (ω) and radius (r), it experiences a radial acceleration ω²r directed towards the center of the path.

Explanation

When a weightless rubber balloon is filled with 200 cc of water and submerged in water, it experiences no weight. This is because the downward force due to the weight of water inside the balloon is exactly counterbalanced by the upward buoyant force of the surrounding water. This equilibrium results in the balloon having zero weight in water.

Explanation

Explanation: The assertion that the weight of a body decreases with altitude on Earth is true, as gravity weakens with distance from the planet's surface. The reason given, that the Earth is not a perfect sphere, is also true. However, the Earth's shape does not directly cause the decrease in weight with altitude. So, both statements are correct, but the reason does not fully explain the assertion.

Explanation

Topic: Physics Question: When a 4-wheel vehicle is moving at high speed in a sharp circular path, which statements are true? 1) overturn about its outer wheels 2) overturn about its inner wheels 3) skid outwards 4) skid inwards. Options: (a) 1 and 3 (b) 2 and 4 (c) 2 and 3 (d) 1 and 4 Correct: (a) Original: When an object moves in a circular path, it experiences centripetal and centrifugal forces. Rewritten explanation: When an object is in motion along a circular path, it encounters centripetal and centrifugal forces.

Explanation

As an oil tanker with oil starts moving forward on a flat road with constant acceleration, the surface of the oil will tilt with a greater depth at the rear end. This occurs because the tanker's forward motion causes the oil surface to incline in such a way that the rear end has a deeper level compared to the front.

Explanation

In this question, we are asked to determine the effect on the value of g (acceleration due to gravity) on the Earth's surface if the Earth's radius were to shrink by one percent while keeping its mass constant. The formula for calculating g on the Earth's surface is g = GM/R², where G is the gravitational constant, M is the mass of the Earth, and R is the radius of the Earth. If the radius of the Earth were to decrease by one percent, the value of g would increase by two percent. This means that the acceleration due to gravity on the Earth's surface would experience a two percent increase if the Earth's radius were reduced by one percent while its mass remained the same.

Explanation

In this physics question, it is asserted that an iron ball floats on mercury but sinks in water. The reason given is that the specific gravity of iron is greater than that of mercury. The correct option is (c), where the assertion is true but the reason is false. Specific gravity is defined as the ratio of the density of a substance to the density of a reference substance.

Explanation

In this physics problem, a solid cube is placed in water and a 0.2 kg mass is placed on top of it, causing the cube to be completely submerged. When the mass is removed, the cube is 2 cm above the water level. We need to find the length of each side of the cube. To do this, we calculate the volume of the 2 cm portion of the cube using the side length x. The volume is 2x². The mass displaced by this portion is 200 grams. Using the formula Mass = Volume × density, we get 200 = 2x² × 1, which simplifies to x² = 100. Therefore, the length of each side of the cube is 10 cm.

Explanation

In this question, we are given that the mass of a body on earth is 100 kg with an acceleration due to gravity of 10 m/s². If the acceleration due to gravity on the moon is 1/6th of that on earth, then the mass of the body on the moon would still be 100 kg. This is because mass is a universal constant and remains the same regardless of the gravitational force acting on it.

Explanation

When a simple pendulum is set into motion, the acceleration is zero as the bob passes through the mean position. Additionally, in each cycle, the bob achieves a specific velocity twice. It is also true that the amplitude of oscillation of the pendulum decreases over time. Therefore, statements 1, 2, and 4 are correct.

Explanation

The correct representation of one-dimensional uniform motion on a distance-time graph is shown in option (d).

Explanation

A person standing on a surface with no friction can move themselves by whistling. This is because in a system where no external force is present, the momentum remains constant. The correct option is that both assertions are true, but the reason does not provide a correct explanation for the assertion.

Explanation

In a motion picture, typically 24 frames are shown per second throughout the entire film. This is because an image that appears on the retina of the eye remains visible for approximately 0.1 seconds after the stimulus is removed. The correct option is (c) where A is true but R is false.

Explanation

When the hunter fires the gun at the monkey, both the monkey and the bullet are affected by the force of gravity. Therefore, the bullet will hit the monkey at the exact point where it was aimed because both are subject to the same gravitational pull.

Explanation

In this question, a ball is released from the top of a tall building with a constant acceleration of 9.8 m/s². We are asked to find its velocity after 2 seconds. Using the formula v = u + gt, where u is the initial velocity (0 in this case), t is the time (2 seconds), and g is the acceleration (9.8 m/s²), we can calculate the velocity as v = 0 + (9.8 × 2) = 19.6 m/s. Therefore, the correct answer is option (b) 19.6 m/s.

Explanation

Momentum, which is the product of an object's mass and velocity (p = mv), is a vector quantity. This means that momentum has both magnitude and direction, making it different from scalar quantities like pressure, energy, and work.

Explanation

When a girl on a swing changes from a sitting to a standing position, the effective length of the swing decreases. This change in length affects the swing's period, which is calculated using the formula T = 2π√(l/g), where l represents the effective length and g is the acceleration due to gravity. As the effective length decreases when the girl stands up, the period of swing shortens.

Explanation

In the given diagram, a boy at point O throws a ball three times with the same force but at different angles from the ground. The outcomes are shown in the diagram. The correct conclusion is that the greater the initial inclination, the greater the height reached by the ball. This is because the maximum height reached, ymax, is calculated using the formula ymax = (v² sin² θ)/(2g), where v is the initial velocity of the ball, θ is the angle of projection, and g is the acceleration due to gravity. Therefore, as per the equation, a larger initial inclination results in a greater height reached by the ball.

Explanation

In the diagram provided, a body starts from rest on a smooth inclined plane angled at θ with the horizontal. The body accelerates down the incline at a rate of g sin θ. The time it takes for the body to reach the bottom of the incline is calculated as t = 1/(sin θ) √(2h/g).

Explanation

When a liquid flows smoothly through a cylindrical pipe, maintaining consistent velocity and direction at every point, it is considered to have a streamlined flow. In this scenario, the flow profile aligns with option (a), where parallel lines indicate the fastest flow in the center of the pipe.

Explanation

In the scenario of a particle falling freely under gravity from rest, the relationship between displacement (d) and time (t) is correctly depicted in the graph. The correct representation is that displacement is proportional to time, as shown in option (a). This is because the equation for displacement in this case is d = (1/2)gt², where 'g' is the acceleration due to gravity and 'u' (initial velocity) is 0. Therefore, when u=0, d simplifies to ½ gt², indicating that displacement is directly proportional to the square of time.

Explanation

In the field of Physics, a simple machine is a device that alters the direction or strength of a force. Therefore, a simple machine assists individuals in accomplishing the same amount of work using less force.

Explanation

When a parachutist jumps from a height, his speed initially increases as he falls through the distance, and then it reaches a constant speed. Therefore, the relationship between falling speed (v) and distance fallen (d) is best represented by a graph where v is proportional to the square of d, as shown in option (d).

Explanation

Brahmagupta, an Indian mathematician and astronomer, authored several significant books on mathematics and astronomy. He predicted Newton's theory by stating that all objects are attracted towards the earth.