Friction — Set 6
Physics · घर्षण · Questions 51–60 of 60
Which of the following helps to reduce drag on a bird flying through the air?
Correct Answer: D. Streamlined body
A streamlined body shape allows air to flow smoothly around the bird, reducing air resistance or drag. This energy-efficient design is essential for long-distance migration. Humans copy this design for aircraft and high-speed trains.
The force of friction does NOT depend on which of the following?
Correct Answer: B. Apparent area of contact
For most dry solid surfaces, the force of friction is independent of the apparent area of contact. Whether a brick is sliding on its wide side or narrow side, the friction remains the same if the weight is constant. This is a fundamental principle known as Amontons's First Law.
Why is sand often spread on tracks covered with snow?
Correct Answer: D. To increase friction
Sand increases the roughness of the slippery snow-covered surface, thereby increasing friction. This extra friction provides the necessary grip for vehicle tires to move without spinning. It is a common safety measure in cold climates during winter.
What happens to the friction between two surfaces if they are polished excessively?
Correct Answer: D. It may increase due to adhesion
Excessive polishing can actually increase friction because the surfaces become so flat that molecular attraction (adhesion) increases. This is particularly noticeable with very clean, flat metals. In most daily cases, however, polishing is used to reduce friction.
Which of the following is an example of sliding friction?
Correct Answer: C. A child on a playground slide
A child sliding down a playground slide is a classic example of sliding or kinetic friction. The surface of the child's clothes rubs against the surface of the slide. This friction helps control the speed of the descent.
The 'coefficient of friction' is usually represented by which Greek letter?
Correct Answer: A. Mu
The Greek letter 'mu' (μ) is the standard symbol used in physics to represent the coefficient of friction. It is a ratio and therefore has no units. There are different mu values for static and kinetic friction for any given pair of surfaces.
Why do carrom players use powder on the board?
Correct Answer: B. To reduce friction for the coins
Powder acts as a lubricant by filling in the microscopic irregularities of the wooden board. This significantly reduces the friction, allowing the striker and coins to move smoothly. It is an effective way to improve the gameplay by increasing speed.
Which of these is a way to increase friction when it is needed?
Correct Answer: C. Treading of tires
Treading or grooving tires increases their grip on the road by increasing friction and allowing water to escape. This is vital for road safety, especially in wet or muddy conditions. Without treads, cars would easily slip and lose control.
The resistance offered by a gas or a liquid to the motion of an object is called _____.?
Correct Answer: A. Viscosity
Viscosity is the internal friction within a fluid that resists flow or the motion of objects through it. Thick liquids like honey have high viscosity compared to water. It is a key factor in determining fluid friction or drag.
When we rub our hands together, they become warm due to _____.?
Correct Answer: A. Friction
Rubbing hands together generates heat because of the friction between the skin surfaces. The mechanical work done by our muscles is converted into thermal energy. This is a common way to quickly warm up cold hands.