Presentation on theme: "Kinetic Energy and Gravitational Potential Energy We can rewrite"— Presentation transcript:
1Kinetic Energy and Gravitational Potential Energy We can rewrite Chapter 10 EnergyKinetic Energy and Gravitational Potential EnergyWe can rewrite
2Kinetic Energy:We define K = ½ mV2Unit of kinetic energy (Kg m2/s2) JouleEx. For a mass 0.5 Kg, V = 4m/s, K = 4JGravitational potential energy:• We define Ug=mgy• Unit of potential energy: Joule• Kinetic energy never be negative.• gravitational potential energy depends on the position.
3Example 10.3 P275 Example 10.4 P276 Example 10.8 P283 Stop to think P273 Stop to think P275 Stop to think P278 Stop to think P280 Stop to think P284 Stop to think P292Example P275Example P276Example P283Example P286Example P291
10Quick thinkA small child slides down the four frictionless slides A-D. Each has the same height.Rank in order. From largest to smallest her speeds VA to VD at the bottom.VA = VB =VC =VD
11Ex A ballistic pendulum A 10 g bullet is fired into a 1200g wood block hanging from a 150-cm-long string. The bullet embeds itself into the block, and block then swings out to an angle of 40o. What was the speed of the bullet?The momentum conservation equationPi = Pf applied to the inelastic collisionThen turning our attention to the swingThe energy equationKf + Ugf = Ki + UgiWe define y1 = 0Get:
12Three identical balls are thrown from the top of a building, all with the same initial speed the first is thrown horizontally, the second at some angle above the horizontal and third at some angle below the horizontal. Neglecting the air resistance, rank the speeds of the balls at the instant each hits the ground.Answer: All the three balls have the same speed at the moment they hit the ground.Since neglect the air resistance, total mechanical energies for each ball should be conserved.Ki+Ui= 1/2mvi2 +mghKf + Uf = 1/2mvf2Ki+Ui = Kf +UfVf2= 2gh + vi2 does not matter the angle.Three balls take different times to reach the ground