**Unformatted text preview: **t = 0 and t = 2. ⇒ 6. The observation deck on the 102nd ﬂoor of the Empire State Building is 1,224 feet above the ground. If a steel ball is dropped from the observation deck its velocity at time t is approximately v ( t ) =-32 t feet per second. Find the average speed between the time it is dropped and the time it hits the ground, and ﬁnd its speed when it hits the ground. ⇒ 9.5 Work A fundamental concept in classical physics is work : If an object is moved in a straight line against a force F for a distance s the work done is W = Fs . EXAMPLE 9.12 How much work is done in lifting a 10 pound weight vertically a distance of 5 feet? The force due to gravity on a 10 pound weight is 10 pounds at the surface of the earth, and it does not change appreciably over 5 feet. The work done is W = 10 · 5 = 50 foot-pounds....

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