John starts at his locker and walks past his 3rd period class straight to his friends locker that is 27 m away. It takes him 14 seconds to get to his friends locker. After hearing the bell ring, he quickly goes back to his classroom 18 m away in 8 seconds.

d

explanation:

v=uf/(u-f)

= 5.10/(5-10) convex lens has positive focal length

=50/-5

=-10 cm (formed at other side)

battery with hi vtge high val resist in series

wavelength divides in half and speed stays the same.

305.7

explanation:

density =m/v

density =917/3.00

density = 305.

approximately = 305.7

in four significant figures