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Introductory Physics Homework Help
Finding Final Velocity or Setting it Equal to 0(Kinematics)
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[QUOTE="TSny, post: 5861431, member: 229090"] This causes a lot of confusion. Different instructors sometimes use different conventions here. So, I'm not sure what your instructor uses. My preference is to always use the symbol g to represent the [I]magntitude[/I] of the acceleration of gravity. So, g is always a positive number whether you take upward as positive direction or downward as positive direction. g = 9.8 m/s[SUP]2[/SUP] near the Earth's surface. The velocity equation for the y-direction is v[SUP]2[/SUP][SUB]yf[/SUB] = v[SUP]2[/SUP][SUB]yi[/SUB] + 2a[SUB]y[/SUB]Δy. You have a choice of taking the positive direction for y to be upward or downward. But you must make a choice and stick with it. If you take upward as positive, then the acceleration due to gravity is negative (since the acceleration is downward). Thus, a[SUB]y[/SUB] = -g = -9.8 m/s[SUP]2[/SUP]. The equation is then v[SUP]2[/SUP][SUB]yf[/SUB] = v[SUP]2[/SUP][SUB]yi[/SUB] + 2a[SUB]y[/SUB]Δy = v[SUP]2[/SUP][SUB]yi[/SUB] + 2(-g)Δy So, v[SUP]2[/SUP][SUB]yf[/SUB] = v[SUP]2[/SUP][SUB]yi[/SUB] - 2gΔy where g = 9.8 m/s[SUP]2[/SUP] (But again, there are those who prefer to define g as a negative number for the case where upward is taken as positive. This is fine as long as it is treated properly when used in the equations.) I think the safest thing to do is always write the equation as v[SUP]2[/SUP][SUB]yf[/SUB] = v[SUP]2[/SUP][SUB]yi[/SUB] + 2a[SUB]y[/SUB]Δy . If you are dealing with a projectile problem where you choose upward as positive, then just make sure you plug in a negative number for a[SUB]y[/SUB]. [/QUOTE]
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Introductory Physics Homework Help
Finding Final Velocity or Setting it Equal to 0(Kinematics)
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