# webct5 - W from a 1 A particle with an initial velocity v(t...

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W from a 1. A particle with an initial velocity v ( t = 0) = 7.5 m/s i has a constant acceleration a = –3 m/s 2 i. At t = 0, its kinetic energy is 30 J. Find the kinetic energy of the particle at t = 2 s. To calculate final KE we need to know the final velocity: 2 0 ˆˆ ˆ (7.5 m/s) ( 3 m/s )(2 s) 1.5 m/s vv a t i i i =+= + = GG G and the mass of the particle, which can be derived from its kinetic energy at t = 0: 2 0 00 22 0 2 12 ( 3 0 J ) 1.1 kg 2( 7 . 5 m / s ) K Km v m v =⇔ = = = 11 Thus, ( 2 s) (1.1 kg)(1.5 m/s) 1.2 J f Kt m v == = = 2. Find the kinetic energy of the particle at t = 4 s. Same procedure: 2 0 ˆ (7.5 m/s ) ( 3 m/s )(4 s) 4.5 m/s Thus, ( =4 s) (1.1 kg)( 4.5 m/s) 11 J f t i i i m v + = = 3. Find the net work done on the particle between t = 0 and t = 2 s. net 1.2 J 30 J 28.8 J WK =∆ = =− 4. Find the net work done on the particle between t = 2 s and t = 4 s. net 11 J 1.2 J 9.8 J = 5. Find the net work done on the particle between t = 0 and t = 4 s. net net 11 J 30 J 19 J Or: 28.8 9.8 19 J W + =

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James Bond 1. After stopping at the cliff, James Bond (90 kg) finds out that it was not a cliff but just a steep slope that a secret spy like him can easily handle. He lets himself go from rest and smoothly slides down the h = 15 m high hill. A big parking lot lies at the bottom of the hill. Since the parking area has been cleared of snow, the friction between the ground and the skis brings our hero to a halt at point D, located at a distance d = 12 m from point C . The descent can be considered frictionless.
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webct5 - W from a 1 A particle with an initial velocity v(t...

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