 # Review.  What is it called when the speed of an objects changes?

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Review

 What is it called when the speed of an objects changes?

 What’s the difference between speed and velocity?

 What is the speed of a car that traveled 125 miles in 2 hours?  Hint: Make sure you include units!  Do NOT ROUND!

 d = 125 miles  t = 2 hours  v = ?  v = d/t  v = 125 miles/2 hours  v = 62.5 mi/hr OR 62.5 mph

 How much time does it take for a bird flying at a speed of 45 mph to travel a distance of 1800 miles?  Hint: Calculate time in minutes

 v = 45 mi/hr  d = 1800 miles  t = ?  V = d/t  t = d/v  t = 1800 miles/45 mph  t = 40 hours  t = 40 hr *(60min/1 hr) = 2400 min

 What is the acceleration due to gravity = to?

 _______________ speed is speed at any moment.  Hint: The speedometer in a car measures this.

 A car accelerates from 25 km/hr to 55 km/hr in 30 minutes. What is its acceleration?  Hint: Make sure your units are km/hr 2

 v i = 25 km/hr  v f = 55 km/hr  t = 30 min  a = ?  a = (v f – v i )/t  a = (55 -25)/0.5 hr  a = 60 km/hr 2

s

 Constant Velocity  Slope = rise/run =Δy/Δx  Slope = dist/time  Slope = (50-0)/(5-0)  Slope = 10 m/s

 What do we mean when we say motion is relative?

 A train is accelerating at a rate of 2 m/s 2. If its initial velocity is 20 m/s, what is its velocity after 30 seconds?

 a = 2 m/s2  v i = 20 m/s  t = 30 sec  v f = ?  a = (v f – v i )/t  2 = (v f – 20)/30  30*2 = v f – 20  60 = v f – 20  80 m/s = v f

 On the Moon, ALL objects accelerate at the same rate.

 Draw the path of an object being thrown up and coming back down (free fall). Show what happens to speed when:  It’s going up  At the top  Coming back down

 Suppose that a ball is dropped from a tower 70.0m high. How far will it have fallen after 1.00 s, 2.00 s, and 3.00 s? Neglect air resistance.

 g = 10 m/s 2  t = 1 s, 2 s, 3 s  d = ½ *g*t 2  d = ½ * 10 m/s 2 * (1 s) 2  d = 5 m/s 2 * 1 s 2  d = 5 m  d = ½ * 10 m/s 2 * (2 s) 2  d = 5 m/s 2 * 4 s 2  d = 20 m  d = ½ * 10 m/s 2 * (3 s) 2  d = 5 m/s 2 * 9 s 2  d = 45 m

 Suppose an object is thrown downward with an initial velocity of 3.0 m/s, instead of being dropped. What would its speed be after 1.0 s and 2.0 s?  Hint: Use v f = v i + a*t

 v i = 3 m/s  t = 1 s, 2 s  g = 10 m/s 2  v f = ?  v f = vi + a * t  v f = 3 m/s + (10m/s 2 * 1 s)  v f = 3 m/s + 10 m/s  v f = 13 m/s  v f = 3 m/s + (10m/s 2 * 2 s)  v f = 3 m/s + 20 m/s  v f = 23 m/s

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