Question

1. which of the following is an example of conduction?

a) sun warming your skin
b) boiling water in a pot
c) metal spoon heating in coffee
d) warm air rising in a room

1. which of the following is a closed system?

a) an open cup of coffee
b) a boiling pot without a lid
c) a cup of coffee with a lid
d) the atmosphere

1. which energy transformation happens when a person eats food and then runs?

a) chemical to mechanical
b) mechanical to heat
c) electrical to light
d) gravitational to sound

1. in a closed system, the total amount of energy:

a) always increases
b) always decreases
c) remains constant
d) disappears

1. which type of heat transfer does not require a medium or direct contact?

a) conduction
b) convection
c) radiation
d) friction

Explanation:

• Question 21: Conduction is heat transfer through direct contact. A metal spoon in coffee (C) shows conduction as heat moves from coffee (hot) to spoon (cold) via direct contact. Sun warming skin (A) is radiation. Boiling water (B) and warm air rising (D) are convection.
• Question 22: A closed system exchanges energy but not matter. A cup of coffee with a lid (C) is closed (no matter exchange, can exchange heat). Open cup (A), boiling pot without lid (B) exchange matter. Atmosphere (D) is complex and not a simple closed system.
• Question 23: Food has chemical energy. When a person eats and runs, chemical energy (from food digestion) is transformed to mechanical energy (for movement). So it's chemical to mechanical (A).
• Question 24: In a closed system, according to the law of conservation of energy, the total energy remains constant (C). It doesn't increase (A), decrease (B), or disappear (D).
• Question 25: Radiation (C) can transfer heat through vacuum (no medium). Conduction (A) needs direct contact (medium - solids mainly). Convection (B) needs a fluid medium (liquids/gases). Friction (D) is not a heat - transfer type (it's a force that causes heat generation).

Answer:

1. C. Metal spoon heating in coffee
2. C. A cup of coffee with a lid
3. A. Chemical to mechanical
4. C. Remains constant
5. C. Radiation