contestada

A 2.0-kg mass is projected from the edge of the top of a 20-m tall building with a velocity of 24 m/s at some unknown angle above the horizontal. Disregard air resistance and assume the ground is level. What is the kinetic energy of the mass just before it strikes the ground? Answer: 0.97 kJ.

Respuesta :

georgestirban

Ox:vā‚“=vā‚€

x=vā‚€t

Oy:y=h-gtĀ²/2

|vy|=gt

tgĪ±=|vy|/vā‚“=gt/vā‚€=>t=vā‚€tgĪ±/g

y=0=>h=gtĀ²/2=vā‚€Ā²tgĀ²Ī±/2g=>tgĪ±=āˆš(2gh/vā‚€Ā²)=āˆš(2*10*20/24Ā²)=āˆš(400/576)=0.83=>Ī±=tgā»Ā¹0.83=39Ā°

cosĪ±=vā‚“/v=vā‚€/v=>v=vā‚€/cosĪ±=24/cos39Ā°=24/0,77=31.16 m/s

Ec=mvĀ²/2=2*31.16Ā²/2=971.47 J=>Ecā‰ˆ0.97 kJ

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