PHYSICS 209 Lecture 12: HW12Solutions

A girl, moving at 8 m/s on in-line skates, is overtaking a boy moving at 5 m/s as they both skate on a straight-line path. The boy tosses a ball backward toward the girl, giving it a speed of 12 m/s relative to him. What is the speed of the ball relative to the girl, who catches it?

(a) (8 + 5 + 12) m/s

(b) (8 - 5 - 12) m/s

(c) (8 + 5 - 12) m/s

(d) (8 - 5 + 12) m/s

(e) (-8 + 5 + 12) m/s

How does a 12-month lunar calendar differ from our 12-month solar calendar?

The number of atoms in 12 g of Carbon 12 is defined as one mole. That number is about 6.022×1023 atoms in one mole. What is the mass of one atom of Carbon 12 in kg?