Can someone help me on number 15? I don’t understand

Iknow #2 is d. i just need to know why

The twister and runaway train are two coasters at the same amusement park. both coasters start at the same height. the coaster for the twister is twice the mass of the coaster for the runaway train. which roller coaster has greater gravitational potential energy at the start of the ride?

Draw the structure for 5-isopropyl-2-methyl-3-nonene