Newton's first law
a. describes how an object accelerates when a force is applied
b. says that objects eventually stop unless a force is applied
c. says that objects with mass attract each other
d. forces come in action/reaction pairs
e. an object will remain in uniform motion unless acted upon by a force
f. like charges repel, opposite charges attract

Aspring has a relaxed length of 33 cm (0.33 m) and its spring stiffness is 6 n/m. you glue a 76 gram block (0.076 kg) to the top of the spring, and push the block down, compressing the spring so its total length is 15 cm. you make sure the block is at rest, then at time t=0 you quickly move your hand away. the block begins to move upward, because the upward force on the block by the spring is greater than the downward force on the block by the earth. calculate y vs. time for the block during a 0.09-second interval after you release the block, by applying the momentum principle in three steps each of 0.03-second duration.