A student has an 80 g sample of a radioactive material that has a half-life of 20 seconds. How much material will he have left after 60 seconds? A.
10 g

B.
20 g

C.
40 g

D.
5 g

Which statement best explains why an object weight less on mercury than it does on earth

Using a pedometer, you walk 3000 steps in 20 minutes, so your speed is 150 steps/min. each of your steps is 0.7 m long. what is your speed? 150 steps/min=/s=/h

Astone weighing 1.5 kilograms is resting on a rock at a height of 20 meters above the ground. the stone rolls down 10 meters and comes to rest on a patch of moss. the gravitational potential energy of the stone on the moss is joules.