Work and energy — Flashcards
Telangana Board · Class 9 · Physical Science
20 flashcards for Work and energy (Telangana Board Class 9 Physical Science) to test yourself on key terms and facts.
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A boy pushes a heavy box with 50N force for 3 meters. Calculate the work done.
Answer
Work = Force × Displacement W = F × s = 50N × 3m = 150 J Work done is 150 Joules because force and displacement are in the same direction.
Why does a porter carrying luggage on his head while standing still do no work according to science?
Answer
Scientific work requires two conditions: (1) Force must be applied, and (2) Object must be displaced. The porter applies force but luggage doesn't move, so displacement = 0. Since Work = Force × Displ…
Calculate the kinetic energy of a bicycle (total mass 60 kg) moving at 5 m/s.
Answer
Kinetic Energy = ½mv² KE = ½ × 60 kg × (5 m/s)² KE = ½ × 60 × 25 = 750 J The bicycle has 750 Joules of kinetic energy.
What happens to energy when a ball is thrown upward and reaches maximum height?
Answer
At ground: Maximum kinetic energy, minimum potential energy During flight: KE decreases, PE increases At maximum height: KE = 0, PE = maximum Total mechanical energy remains constant (conservation of …
A 2 kg book is lifted 1.5 m high. Calculate its potential energy. (g = 10 m/s²)
Answer
Potential Energy = mgh PE = 2 kg × 10 m/s² × 1.5 m PE = 30 J The book gains 30 Joules of gravitational potential energy.
Why can a moving bullet pierce through a wooden plank but a stationary bullet cannot?
Answer
Moving bullet has kinetic energy (KE = ½mv²) which can do work on the plank. The kinetic energy gets converted to work in breaking through the wood fibers. Stationary bullet has no kinetic energy, so …
A machine does 1200 J of work in 4 minutes. Calculate its power.
Answer
Power = Work/Time Time = 4 min = 4 × 60 = 240 s P = 1200 J ÷ 240 s = 5 W The machine's power is 5 Watts.
How does a bow and arrow demonstrate potential energy?
Answer
When bow string is stretched, work is done against elastic force. This work gets stored as elastic potential energy in the stretched bow. When released, potential energy converts to kinetic energy of …
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