Ways of thermal transfer
Which type of heat transfer requires direct contact between particles?
Conduction
What is the formula for calculating work done by a force?
W=F×d (work = force × distance in the direction of the force)
What is the main difference between kinetic energy and potential energy?
Kinetic energy (KE) is the energy of motion.
Potential energy (PE) is stored energy due to position or condition.
What does the law of conservation of energy state?
Energy cannot be created or destroyed; it can only change from one form to another. The total energy in a closed system remains constant.
When you boil water, bubbles rise and cooler water sinks. Which type of heat transfer is responsible for this motion, and why?
Convection, because heated water becomes less dense and rises while cooler, denser water sinks, creating a circulation current.
A student pushes a box with a force of 50 N for a distance of 2 m. How much work is done if the force is applied horizontally and friction is ignored?
W = 50 × 2 = 100 J
A roller coaster moves from the top of a hill down to the bottom. How does the total mechanical energy (KE + PE) of the coaster affected, if friction is ignored?
The total mechanical energy stays constant; potential energy decreases as kinetic energy increases. Energy is conserved.
A car’s engine burns fuel to move the car, but some energy is lost as sound and heat. Is energy lost from the universe? Explain.
No — energy isn’t lost; it’s transferred into less useful forms (heat, sound). The total energy stays the same, but it’s spread out and harder to use (lower-quality energy).
You’re camping on a cold night. You feel warmth when facing the fire, but not when you turn around, even though the air temperature is the same. Which type of heat transfer is mainly responsible, and why?
Radiation, because infrared waves travel in straight lines from the fire and don’t heat the air much; your back isn’t facing the radiating source.
Which simple machine is used in a seesaw, crowbar, and scissors?
Lever
When a pendulum swings from its highest point to the lowest, describe how energy changes. Why does the pendulum eventually stop?
Energy continually transforms between potential and kinetic energy. At the highest point, energy is mostly potential; at the lowest, mostly kinetic. It eventually stops because some mechanical energy is converted to heat and sound due to air resistance and friction
Describe how energy transfers and transformations occur when solar energy powers a moving electric car.
Sunlight (radiant energy) → Electrical energy (in solar cells)
Electrical energy → Chemical energy (stored in battery)
Chemical energy → Kinetic energy (motion of car) + Heat (in wires, motor)
Two identical pots, one made of aluminum and one of stainless steel, are placed on equal burners. The water in the aluminum pot boils first. Explain why, in terms of conduction and specific heat.
Aluminum has higher thermal conductivity and lower specific heat, transferring energy faster and requiring less energy to raise its temperature, so water heats faster.
A pulley system is used to lift a 100 N load. If the system has an ideal mechanical advantage (IMA) of 2, how much effort force is needed to lift the load (ignore friction)?
Effort=MA / Load=2/100=50 N
A student claims, “A heavy truck moving slowly has the same kinetic energy as a small car moving fast.”
How could you evaluate this statement without doing any calculations?
You’d reason that both mass and speed affect kinetic energy. A truck’s large mass may balance a car’s high speed, so it’s possible if the car’s velocity compensates for its small mass — but only measurements would confirm it.
If energy is always conserved, why does a bouncing ball never return to its original height after each bounce?
Because some of the mechanical energy is converted to heat, sound, and internal deformation each time it hits the ground.
At night, deserts become very cold even after hot days. Explain this large temperature drop using ideas of radiation and conduction.
During night, ground and air lose energy by infrared radiation to space, and dry sand (poor conductor) cannot retain or transfer heat from deeper layers—so surface cools quickly.
Two students lift identical boxes to the same height — one does it quickly, the other slowly. Who does more work?
Both do the same amount of work; work depends only on force and distance, not on time. The faster student, however, produces greater power.
Why can a moving bullet have more kinetic energy than a speeding truck?
Because kinetic energy depends on mass and the square of velocity. The bullet’s mass is tiny, but its speed is extremely high — velocity squared can make up for the small mass.
Why does a bouncing ball never return to its original height after each bounce, even though energy is conserved?
Because some of the mechanical energy is converted to heat, sound, and internal deformation each time it hits the ground. The total energy (including these forms) is conserved, but useful mechanical energy decreases