Một vật dao động điều hòa dọc theo trục Ox (O là vị trí cân bằng) có phương trình: x = 2cos(2πt + π/2) (cm). Hỏi sau thời gian bao lâu thì vật đi được quãng đường 99 cm kể từ thời điểm ban đầu t = 0 ?

Three different objects, all with different masses, are initially at rest at the bottom of a set of steps. each step is of uniform height . the mass of each object is a multiple of the base mass : object 1 has mass 4..00m , object 2 has mass 1..96m , and object 3 has mass . when the objects are at the bottom of the steps, define the total gravitational potential energy of the three-object system to be zero. if the objects are then relocated as shown, what is the new total potential energy of the system? each answer requires the numerical coefficient to an algebraic expression. each algebraic expression is given using some combination of the variables , , and , where is the acceleration due to gravity. enter only the numerical coefficient. (example: if the answer is 1..23mgd , just enter 1.23)

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Explain what it means to view something from a frame of reference. provide an example that illustrates your explanation. (4 points)