(e) The mouse changes direction when changes sign. This happens at and 9.0 s. (f) The mouse is speeding up when is increasing. This happens for and for The mouse is slowing down when is decreasing. This happens at for and for The mouse is instantaneously at rest at and (g) No. These formulas apply only when the acceleration is constant. For constant acceleration the graph of versus t is a straight line and that is not the case here. Reflect: When and have the same sign, the speed is increasing. When and have opposite signs, the speed is decreasing. When the speed is constant. 2.84. Set Up: In time the S-waves travel a distance and in time the P-waves travel a distance Solve: (a) and (b) 2.85. Set Up: and Take to be downward, toward the surface of Mars, and take the origin to be at the surface. Solve: (a) and gives The minus sign signifies that the acceleration is upward. (b) Then gives gives (c) For Stage IV, and Then gives The lander is 24 m above the surface when Stage IV begins. gives
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