Question

simple clarification help- No math!

can someone explain to me why you are able to solve a problem using the law conservation of mechanical energy (KEi + PEgravityi + PEelastici = KEf +PEgravityf + PEelasticf) and solve the same problem with kinematics, yet arrive at the same answer?

Answer 1

law of conservation what you have before = what you have after meaningful.
you mean by kinematics momentum ??can you state the problem to know what do you mean.

Answer 2

so in class we solved this problem: an object is thrown off a 300m high cliff at and angle of 32 degrees with an Vi= 20m/s, what is the Vf? and using law of convs. of mech. energy we found Vf = 79.25 m/s,

We now have to prove we can arrive at the same Vf value solving the problem with kinematics equations but I don't see how that could be possible.

Answer 3

By using the mechanical energy. You didn't look at the path (its conservative) it take.When a body move from high potential energy to low potential energy that means that energy transferred to other form like increasing kinetic energy(you just know the amount of energy lost to be at ground).
By using kinematics. you look at the path it take and you analyze the path i took to reach the ground and you will get the answer because you will use the acceleration and acc. is the measurement of the force and energy is also the measurement of the force.
there is one force and you measure it with different methods, so you get the same result.
kinematics is derivative from acceleration .(force)
Force is derivative from mechanical energy as dE/dt = F.