Air is pumped into a spherical balloon, so the balloon expands. the volume of a sphere of radius r is 4πr3/3. if the radius of the sphere after t seconds is 2t centimeters, at what rate is air being pumped in when t=4? (hint: the rate air is pumped in equals the rate that the volume of the sphere increases).

16. a brave but inadequate rugby player is being pushed backward by an opposing player who is exerting a force of 800 n on him. the mass of the losing player plus equipment is 90.0 kg, and he is accelerating at 1.20m/s2 size 12{1 "." "20"" m/s" rsup { size 8{2} } } {} backward. (a) what is the force of friction between the losing player’s feet and the grass? (b) what force does the winning player exert on the ground to move forward if his mass plus equipment is 110 kg? (c) draw a sketch of the situation showing the system of interest used to solve each part. for this situation, draw a free-body diagram and write the net force equation.