lecture2

lecture2 - 8/26/10 1 Phys 2101 Gabriela Gonzlez 2 Position...

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Unformatted text preview: 8/26/10 1 Phys 2101 Gabriela Gonzlez 2 Position is a vector, function of time: Velocity: v ( t ) = d r ( t ) dt r ( t ) = v ( t ) t dt Acceleration: a ( t ) = d v ( t ) dt = d 2 r ( t ) dt 2 v ( t ) = a ( t ) t dt r ( t ) = x ( t ) i + y ( t ) j + z ( t ) k two, three 8/26/10 2 3 Motion in two dimensions, with constant acceleration: j gt t v x t x j gt v t v j g t a ) ( ) ( ) ( 2 2 1 + = = = g 4 A football player punts the football so that it will have a hang time (time of flight) of 5 s and land 50m away. If the ball leaves the players foot 150cm above the ground, what must be the magnitude and direction of the balls initial velocity? 8/26/10 3 5 A football player punts the football so that it will have a hang time (time of flight) of 5 s and land 50m away. If the ball leaves the players foot 150cm above the ground, what must be the magnitude and direction of the balls initial velocity? a(t) = - 9.8 m/s 2 j v(t) = v 0x i + (v 0y 9.8 t m/s 2 ) j r(t) = v 0x t i + (1.5m + v 0y t 4.9 t 2 m/s 2 ) j We know that at t=5s, r(t)=50m i, so: 50m = v 0x x 5s v 0x = 10 m/s 0m = 1.5m + v 0y 5s 4.9 x 25 s 2 m/s 2 = -121 m/s + v 0y 5s v 0y = 24.2 m/s Velocity magnitude: v= (10 2 + 24.2 2 ) m/s = 26.2 m/s Velocity direction: =atan(24.2/10) = 67.5 o 6 Physics having predictive value! Newtons laws: two qualitative, one quantitative: 1. If no net force, no acceleration (either at rest, or moving with constant velocity) 2. 3. Action and reaction forces are equal and opposite. a m F = 8/26/10 4 7 g F T F N f Gravitational force : vertical, pointing down, from center of gravity. Normal force : perpendicular to the surface, making total force into the surface zero. Tension : reaction force produced by a string Friction force : produced by the surface, parallel to the surface, opposing motion. 8 The block m 1 does not move. If m 1 =10 kg, what does the spring scale read? What are the magnitude and direction of the normal force? N T m 1 g 8/26/10 5 9 The block m 1 does not move. a) If m 1 =10 kg, what does the spring scale read?...
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This note was uploaded on 12/01/2011 for the course PHYS 2101 taught by Professor Grouptest during the Fall '07 term at LSU.

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lecture2 - 8/26/10 1 Phys 2101 Gabriela Gonzlez 2 Position...

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