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Conservation of Mechanical Energy

Conservation of Mechanical Energy. A 2.5 kg ball hangs from a 30 m massless string. I smack it, so it initially flies horizontally at 15 m/s. What is its speed after the ball has ascended 45°?. ME i = ME f. 0. PE i + KE i = PE f + KE f. 45°. 1/2mv i 2 = mgh f + 1/2mv f 2. 30cos45°.

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Conservation of Mechanical Energy

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  1. Conservation of Mechanical Energy A 2.5 kg ball hangs from a 30 m massless string. I smack it, so it initially flies horizontally at 15 m/s. What is its speed after the ball has ascended 45°? MEi = MEf 0 PEi + KEi = PEf + KEf 45° 1/2mvi2 = mghf + 1/2mvf2 30cos45° 30 m h h = 30m – 30cos45° = 8.79 m vf = 7.25 m/s SMACK!! How high will it go? 11.47 m

  2. Work-Kinetic Energy Theorem A 2000 kg car travelling 50 km/h slams on the brakes. If the tires provide a frictional force of 5000 N, at what distance does the car stop? W = DKE 50 km/h = 13.9 m/s 0 Fd = 1/2mvf2 – 1/2mvi2 d = 38.6 m

  3. A wagon with passengers has a mass of 40 kg as it travels at 4 m/s over a hill as shown. Find the velocity at point b. Assume there is no friction. 4 m/s MEi = MEf 0 J mghi + 1/2mv2i = mghf + 1/2mv2f v2f = 2ghi + v2i vf = 24.6 m/s 30 m c 14 m b Find the velocity at point c. mghi + 1/2mv2i = mghf + 1/2mv2f 2(ghi – ghf)+ v2i = v2f vf = 18.2 m/s

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