We now have two powerful tools we can use to analyze physical situations. We can
ID: 1436222 • Letter: W
Question
We now have two powerful tools we can use to analyze physical situations. We can either combine a force analysis with the constant acceleration equations, or we can use a conservation of energy analysis In certain situations, one method may be preferred over the other, and in other cases either method will work. Consider the following situations, and the methods you would use to analyze them. In each case, choose all the statements that apply. A block slides down a frictionless incline, which has a constant slope. We know the height and length of the incline, as well as the angle at which it is inclined. If we want to know how much time it takes the block to slide down, after being released from rest, We can use a force analysis to find the acceleration, and then use that acceleration in a constant-acceleration equation. It's difficult to apply a force analysis, because the acceleration is not constant. A conservation-of-energy analysis all by itself would get us the answer. Conservation of energy by itself would not be enough. Consider the same situation as in part (a). If we want to know the block's speed at the bottom of the incline, which method should we use? Select all the statements that apply. We can use a force analysis to find the acceleration, and then use that acceleration in a constant-acceleration equation. It's difficult to apply a force analysis, because the acceleration is not constant. A conservation-of-energy analysis all by itself would get us the answer. Conservation of energy by itself would not be enough. A boy slides down a frictionless water slide. Like most water slides, the slide does not come down in a straight line - instead, the slide is curved, and some parts of it are steeper than other parts. We know the height through which the boy drops, after starting from rest. If we want to know the boy's speed at the bottom of the slide, which method should we use? Select all the statements that apply. We can use a force analysis to find the acceleration, and then use that acceleration in a constant-acceleration equation. It's difficult to apply a force analysis, because the acceleration is not constant. A conservation-of-energy analysis all by itself would get us the answer. Conservation of energy by itself would not be enough.Explanation / Answer
a) first and fourth statement,
we can use force analysiso find the acceleration, and use it in constant acceleration equation,
In this case energy doesn't deal with time so we can not use enery equation.
Acceleration is constant, a = gsin theta in such cases
b)first and third statement
we can use force analysiso find the acceleration, and use it in constant acceleration equation, then speed at bottom
we can also apply energy consevation
c)second and third statement are correct,
force analysis cant be applied as acceleration is non uniform because of different slopes,
Energy conservation can be applied because it is fictionless surface
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