Work and Energy — Flashcards
Maharashtra Board · Class 9 · Science
22 flashcards for Work and Energy (Maharashtra Board Class 9 Science) to test yourself on key terms and facts.
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What is the scientific definition of work? When is work said to be done?
Answer
Work is said to be done when a force applied on an object causes displacement of the object. Formula: Work = Force × Displacement. Work is only done when there is movement in the direction of the appl…
What is the formula for work when force and displacement are at an angle θ to each other?
Answer
W = F × s × cos θ, where W is work, F is applied force, s is displacement, and θ is the angle between force and displacement directions.
What are the SI and CGS units of work? How are they related?
Answer
SI unit: Joule (J) = 1 Newton × 1 metre. CGS unit: Erg = 1 dyne × 1 centimetre. Relationship: 1 Joule = 10⁷ erg…
When is work positive, negative, and zero? Give examples.
Answer
Positive work: Force and displacement in same direction (θ = 0°), e.g., pushing a cart forward. Negative work: Force and displacement in opposite directions (θ = 180°), e.g., applying brakes. Zero wor…
Define energy. What is its relationship with work?
Answer
Energy is the capacity of a body to perform work. Energy and work have the same units (Joule in SI, erg in CGS). The work done on an object equals the energy transferred to it.
What is kinetic energy? Derive its formula.
Answer
Kinetic energy is the energy an object has due to its motion. Formula: K.E. = ½mv², where m is mass and v is velocity. Derived from work-energy theorem: Work done = Force × displacement = ma × ½at² = …
A stone of mass 250 g falls with velocity 2 m/s. Calculate its kinetic energy.
Answer
Given: m = 250 g = 0.25 kg, v = 2 m/s. K.E. = ½mv² = ½ × 0.25 × (2)² = ½ × 0.25 × 4 = 0.5 J…
What is potential energy? Give its formula and examples.
Answer
Potential energy is the energy stored in an object due to its position or state. Formula: P.E. = mgh, where m is mass, g is acceleration due to gravity, h is height. Examples: water in overhead tank, …
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