A person holds a 4.0 kg block at position A, 30 cm above ground, in contact with an uncompressed vertical spring with a spring constant of 500 N/m. the person gently lowers the block from rest at position A to rest at position B. which of the following describes the change in the energy of the block-spring-Earth system as a result of the block being lowered?
(a) The energy decreases by approx. 1.5 J
(b) The energy decreases by approx. 2.5 J
(c) The energy increases by approx. 4.0 J
(d) The energy of the system does not change.

Aplayground merry-go-round has a radius of 4.6 m and a moment of inertia of 200 kg-m2 and turns with negligible friction about a vertical axle through its center. a child applies a 26.0 n force tangentially to the edge of the merry-go-round for 15.0 seconds. if the merry-go-round is initially at rest, how much work did the child do on the merry-go-round?

Astudent throws a water balloon with speed v0 from a height h = 1.76 m at an angle θ = 21° above the horizontal toward a target on the ground. the target is located a horizontal distance d = 9.5 m from the student’s feet. assume that the balloon moves without air resistance. use a cartesian coordinate system with the origin at the balloon's initial position. (a) what is the position vector, rtarge t, that originates from the balloon's original position and terminates at the target? put this in terms of h and d, and represent it as a vector using i and j. (b) in terms of the variables in the problem, determine the time, t, after the launch it takes the balloon to reach the target. your answer should not include h. (c) create an expression for the balloon's vertical position as a function of time, y(t), in terms of t, vo, g, and θ. (d) determine the magnitude of the balloon's initial velocity, v0, in meters per second, by eliminating t from the previous two expressions.

Directions: count the number of atoms. ar co2 na3po4 so3 nac2h3o2