This is the periodic table of the elements. Luis made a table of some of the elements and the charges of their ions from period 4. Element Charge K +2 Ca +2 Cr +2 or +3 Se −2 Br −1 According to information in the periodic table, what mistake did Luis make in his table? A The −2 charge for Se is incorrect, because Se is in group 17 which have charges of −1 when they form ions. B The +2 charge for K is incorrect, because K is in group 1 which have charges of +1 when they form ions. C The +2 charge for Cr is incorrect, because Cr is in group 1 which have charges of +1 when they form ions. D The −1 charge for Br is incorrect, because Br is in group 1 which have charges of −2 when they form ions.

Amass m = 74 kg slides on a frictionless track that has a drop, followed by a loop-the-loop with radius r = 18.4 m and finally a flat straight section at the same height as the center of the loop (18.4 m off the ground). since the mass would not make it around the loop if released from the height of the top of the loop (do you know why? ) it must be released above the top of the loop-the-loop height. (assume the mass never leaves the smooth track at any point on its path.) 1. what is the minimum speed the block must have at the top of the loop to make it around the loop-the-loop without leaving the track? 2. what height above the ground must the mass begin to make it around the loop-the-loop? 3. if the mass has just enough speed to make it around the loop without leaving the track, what will its speed be at the bottom of the loop? 4. if the mass has just enough speed to make it around the loop without leaving the track, what is its speed at the final flat level (18.4 m off the ground)? 5. now a spring with spring constant k = 15600 n/m is used on the final flat surface to stop the mass. how far does the spring compress?