12lecture2a08

12lecture2a08 - Physics 2A Lecture 12: Feb 4 Vivek Sharma...

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Physics 2A Lecture 12: Feb 4 Vivek Sharma UCSD Physics
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much to learn may the force be with you at the quiz you still have
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Dynamics Of Particles (Using 2 nd Law) Now examine situations where bodies are accelerating thus not in equilibrium 2 nd law used xx yy Fm a & Fa m m ⇒= = = GG G G
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Ice Sailing With 2 nd Law ! Iceboat at rest. Steady wind pushes the sail. 4s after wind starts, boat’s speed =22km/h. What constant force F W does wind exert on the sail? Mass of boat+sailor = 200kg. Ignore friction . xx 0 x 2 0 x wx xW x Speed v v a t vv a1 . 5 m FF m /s t F ma 300N a =+ ⇒= = = y F0 n m g Normal n = 1960N =⇒ = draw free-body diagram
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Ice Sailing On Surface With Friction Iceboat at rest. Steady wind pushes the sail. Boat accelerates at a x =1.5m/s 2 in presence of constant horizontal frictional force f = 100N. What is F W here ? draw the free-body diagram xW x Wx 2 W Fm a F (200kg)(1.5m/s ) 100N FF m = 4 N a 00 ⇒= + + f f f
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Tension & Weight In An Elevator Woman in elevator moving down with speed 10m/s comes to a stop after decelerating for 25m . If mass of (woman+elevator)=800kg, find the tension T in elevator cord as the elevator decelerates. y yy y FT w m a Elev T ator: wm a = ( g + a ) m ⇒= + ⇒− = 22 y0 y y y 0 2 y 0 y Use v v 2a ( ) vv a2 m / s 2(y y ) T( g + a ) m9 y 0N y 44 =+ = + = What is a y ?
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Apparent Weight In An Elevator A 50.0 kg woman stands on a measuring scale while riding in the elevator. As it decelerates to a stop (a y =2m/s 2 ), what is her weight force ? y y y Fn w m a Wom n an: m=50k m(g a ) 5 N g 90 ⇒= + = ⇒− = As elevator decelerates, scale pushes up on woman with n=590N. Woman pushes down on scale with equal & opp her apparent we o fo ight rce =0 N 59 100N more than her normal weight !! This happens only during deceleration scale reads the magnitude of downward force exerted by the woman on the scale. Use III law Find normal force exerted by elevator
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Monkey (M) & Banana Bunch (B) 20kg monkey holds a massless rope that passes over frictionless pulley attached to 20kg banana bunch. Monkey starts to climb up rope to get it.
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12lecture2a08 - Physics 2A Lecture 12: Feb 4 Vivek Sharma...

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