General Science MCQs – Page 7 (Q61-70)

The maximum height reached by a projectile depends mainly on its initial vertical velocity component, since only the vertical motion is affected by gravity's deceleration, while the horizontal velocity component remains constant throughout the flight, ignoring air resistance. A projectile launched straight up achieves the greatest height for a given speed, while one launched at a low angle travels farther horizontally but reaches a much lower peak. This is why an angle of 45 degrees typically maximizes horizontal range on level ground, balancing vertical and horizontal velocity components equally.

An object moving in a circular path requires a centripetal force directed toward the center of the circle, which continuously changes the object's direction of motion without necessarily changing its speed. Without this inward force, the object would fly off in a straight line tangent to the circle, as described by Newton's first law of inertia. Common sources of centripetal force include gravity for orbiting satellites, tension in a string for a whirled ball, and friction between tires and road for a car turning a corner. Centripetal force should not be confused with the fictitious outward-feeling centrifugal force.

Gravitational force is primarily responsible for keeping planets in orbit around the Sun, continuously pulling each planet inward and acting as the centripetal force that curves their paths into stable elliptical orbits rather than allowing them to travel off in straight lines. Johannes Kepler first described the shapes and timing of these orbits mathematically, and Isaac Newton later explained the underlying gravitational cause. The balance between a planet's forward inertia and the Sun's gravitational pull keeps orbits stable over immense timescales, though gravitational interactions between planets can cause subtle long-term orbital variations.

In a perfectly elastic collision, both momentum and kinetic energy are conserved, meaning no energy is lost to heat, sound, or deformation, and objects typically bounce off each other without any lasting change in shape. True perfectly elastic collisions are rare in everyday life but are closely approximated by interactions between gas molecules or hard steel balls, and are commonly used as idealized models in physics problems. Momentum, however, is always conserved in any collision, whether elastic or inelastic, as long as no external forces act on the system, making it a more universally applicable conservation law.

In an inelastic collision, kinetic energy is generally not conserved because some of it converts into other forms of energy like heat, sound, and permanent deformation of the colliding objects, even though total momentum of the system is still conserved. A perfectly inelastic collision, the most extreme case, occurs when colliding objects stick together and move as one afterward, such as a car crash where vehicles crumple and lock together. Most real-world collisions, from sports impacts to vehicle crashes, fall somewhere between perfectly elastic and perfectly inelastic, losing some but not all kinetic energy.

Impulse experienced by a body is equal to the change in its momentum, a relationship known as the impulse-momentum theorem, which connects the effect of a force acting over time to the resulting change in an object's motion. This is why airbags and padded surfaces reduce injury: by extending the time over which a collision force acts, they reduce the peak force needed to produce the same change in momentum. Impulse is a vector quantity measured in newton-seconds or kilogram-meters per second, the same units as momentum itself.

Impulse can also be calculated as the product of the average force applied and the time duration over which it acts (Impulse = F x t), providing a practical way to analyze forces during brief events like collisions or impacts where force may vary rapidly. This formula explains why follow-through in sports like golf or baseball increases the ball's velocity: extending the contact time increases the impulse delivered for a similar force. Engineers use this principle to design crumple zones in cars, which extend collision time to reduce the force experienced by passengers.

Density of a substance is defined as its mass divided by its volume (density = mass/volume), describing how tightly packed matter is within a given space. Substances with high density, like lead or gold, pack a large mass into a small volume, while substances with low density, like foam or helium gas, have much less mass per unit volume. Density determines whether an object floats or sinks in a fluid, following Archimedes' principle, which is why ice, being less dense than liquid water, floats on top of it, an unusual property among common substances.

Density is measured in kilograms per cubic meter (kg/m cubed) in the SI system, though grams per cubic centimeter or per milliliter is also commonly used in chemistry and laboratory settings. Water has a density of approximately 1,000 kg/m cubed, or 1 gram per cubic centimeter, serving as a useful reference point since substances less dense than water float on it while denser ones sink. Density measurements are essential for identifying unknown substances, verifying material purity, and designing everything from ships' hulls to hot air balloons.

Between a heavier and a lighter object, the heavier object has more inertia, since inertia is directly related to mass: the greater an object's mass, the more it resists changes to its state of motion, whether starting, stopping, or changing direction. This is why it takes much more force to push a loaded truck into motion than an empty shopping cart, and why heavier objects are harder to stop once moving. Inertia is not a force itself but a property of matter, formalized in Newton's first law, and mass is essentially considered the quantitative measure of an object's inertia.