Rita throws a ball straight up into the air and catches it at the same position from which she threw it. the ball has 18 j of mechanical energy when it leaves her hand. if no energy is lost due to friction, which statements about the energy of the ball are true? check all that apply. the potential energy at the top of the ball’s motion is 18 j. the kinetic energy is less when the ball is thrown than when it is caught. the kinetic energy increases as the potential energy decreases. the kinetic energy decreases as the potential energy increases. the total mechanical energy of the ball stays constant. the mechanical energy decreases as the ball moves up and increases as the ball comes down.

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Askydiver weighing 140 lb (including equipment) falls vertically downward from an altitude of 19,000 ft and opens the parachute after 18 s of free fall. assume that the force of air resistance, which is directed opposite to the velocity, is of magnitude 0.55|v| when the parachute is closed and is of magnitude 14|v| when the parachute is open, where the velocity v is measured in ft/s. assume that acceleration due to gravity has magnitude 32 ft/s/s; remember that weight is the product of mass and gravitational acceleration. (a) find the speed of the skydiver when the parachute opens. (b) find the distance fallen before the parachute opens. (c) what is the limiting velocity vl after the parachute opens? (d) determine how long the sky diver is in the air after the parachute opens. (e) plot the graph of velocity versus time from the beginning of the fall until the skydiver reaches the ground.

Ahot-air balloonist, rising vertically with a constant speed of 5.00 m/s releases a sandbag at the instant the balloon is 40.0 m above the ground. after it is released, the sandbag encounters no appreciable air drag. compute the velocity of the sandbag at 0.250 s after its release.