Phys-20 - D. MOTION @ CONSTANT ACCELERATION First look...

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D. MOTION @ CONSTANT ACCELERATION First look cases a = const. and then special case of falling objects. Generally discuss physical laws but not derive mathematically. When a = constant (1) v = v 0 + a t ( no x ) (2) x = v 0 t + ½ a t 2 ( no v ) (3) v 2 = v 0 2 + 2 a x ( no t ) (4) v = ½ ( v + v 0 ) t (no a ) x = displacement; v 0 = initial velocity; v = final velocity a = acceleration; t = elapsed time
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Ex. Car at rest accelerates at 2.0 m/s 2 . After 5.0 s how far moved and what speed? A. Given: a = 2.0 m/s 2 ; t = 5.0 s; hidden information? v 0 = 0 B. Find: x = ?; v = ? C. Choose law to do job for x . x = v 0 t + ½ a t 2 = 0(t) + ½ (2.0m/s 2 ) (5.0s) 2 = 25 m A. Choose law to do job for v . v = v 0 + at = 0 + 2.0 m/s 2 (5.0 s) = 10 m/s
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Ex. Speed car 65mph (29.1m/s); I a I = 3.5m/s 2 Will car hit train? train car v 100 m + A. establish + direction B. v 0 = 29.1 m/s; a = -3.5 m/s 2 C.how do problem? v = 0 & x = ?; or v = ? (100 m) D.select law; v 2 = v 0 2 + 2 a x E. 0 = (29.1m/s) 2 + 2 (-3.5m/s 2 ) x; so x = 121m hit train!
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E. FALLING BODIES
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Phys-20 - D. MOTION @ CONSTANT ACCELERATION First look...

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