Bobby does work to climb to the top of a 7 m hill. If Bobby and his sled have a combined mass of 45 kg, how much Potential Energy will Bobby have at the top of the hill? (Ignore friction in this problem.)

No because scientist are still changing there mines today so they are not correct to this day

The best answer is (a) which is universal law is in effect at all times. it is constantly at play in everything we do and governs our lives. it is also important to note that universal law applies to not only everything on earth, but everything in the universe as well, which is another reason why it is in effect at all times.