P2F11-Week4-Barwick-ans

P2F11-Week4-Barwick-ans - P2 Week 4 Motion in One Dimension...

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P2 Week 4 ü Motion in One Dimension with constant acceleration ü Graphical methods ü Differentiation, slopes, maxima and minima

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Summary for constant acceleration linear motion x-x 0 t-t 0 v v 0 a Equation v = v o + a " (t - t 0 ) x - x 0 = 1 2 v + v o ( ) (t - t 0 ) x " x o = v o (t - t 0 ) + 1 2 a (t - t 0 ) 2 v 2 = v 0 2 + 2 a x " x o ( )
y-y 0 t-t 0 v v 0 a Equation Summary for freely falling objects Up is positive Hence acceleration due to gravity = – g g is the magnitude of acceleration due to gravity Average sea-level value for =9.8m/s 2 . v = v o " g # (t - t 0 ) y " y o = v o (t - t 0 ) " 1 2 g (t - t 0 ) 2 v 2 = v 0 2 " 2 g y " y o ( ) y - y 0 = 1 2 v + v o ( ) (t - t 0 )

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Clicker problem n Raindrops fall 2 km from a cloud to the ground. If they were not slowed by air resistance, how fast would the drops be moving when they struck the ground? Take g=10m/s 2 . n A: 70 km/hr n B: 140 km/hr n C: 500 km/hr n D: 720 km/hr n E: 900 km/hr
Clicker problem n Raindrops fall 2 km from a cloud to the ground. If they were not slowed by air resistance, how fast would the drops be moving when they struck the ground? Take g=10m/s 2 . n Use v 2 =v 0 2 +2 × 10 × 2000 m 2 /s 2 . n Set v 0 =0. n So |v|=200 m/s = 200 × 3600 s / 1000 m × km/hr = 720 km/hr n Having drops fall on your head at this speed would be quite dangerous! n Large raindrops hit terminal speeds of about 40 km/hr in the air.

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Strategy n Precise answers usually require algebraic solutions n Write out equations and solve for unknown n However, more vaguely worded problems may best be solved graphically (See next few problems). n Increase, Bigger, smaller, faster, shorter rather than how big, how fast, how small
Clicker question n How does the vertical distance between them change? n A: increases n B: decreases n C: stays the same n How does the difference in their velocities change? n A: increases n B: decreases n C: stays the same n A skydiver jumps out of a hovering helicopter. A few seconds later, another skydiver jumps out, so they both fall along the same vertical line relative to the helicopter. Both sky divers fall with the same acceleration. Assume that g is constant.

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Clicker question n A skydiver jumps out of a hovering helicopter. A few seconds later, another skydiver jumps out, so they both fall along the same vertical line relative to the helicopter. Both sky divers fall with the same acceleration. n How does the vertical distance between them change? C
Clicker question n A skydiver jumps out of a hovering helicopter. A few seconds later, another skydiver jumps out, so they both fall along the same vertical line relative to the helicopter. Both sky divers fall with the same acceleration. n How does the difference in their velocities change?

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Clicker question- discussed in lecture n How does the vertical distance between them change?
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P2F11-Week4-Barwick-ans - P2 Week 4 Motion in One Dimension...

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