A near-sighted person might correct his vision by wearing diverging lenses with

Question

A near-sighted person might correct his vision by wearing diverging lenses with focal length f = 60 cm. When wearing his glasses, he looks not at actual objects but at the virtual images of those objects formed by his glasses. Suppose he looks at a 14-cm-long pencil held vertically 1.6 m from his glasses. Use ray tracing to determine the location and height of the image. Do this on paper. Your instructor may ask you to turn in this work. location -4367 height 6.11 You observe a bicycle braking from a speed of 5 m/s to rest in 8 s. The bicycle (including the rider) has a mass of 68 kg. What is the magnitude of the net horizontal braking force acting on the bicycle during this time? N

Explanation / Answer

from lens formula

1/f = 1/u +1/v

f = -60 cm for diverging lens

u = 1.6 m

-1/0.6 = (1/1.6) +(1/v)

v = -0.436 m

negative sign indicates the image is infront of the lens

Magnification M = -v/u = hi/ho

0.436/1.6 = hi/14

hi = 3.815 cm

u = 5 m/s, v = 0 , t = 8 s, m = 68 kg

F = ma = m(u)/t

F = 68*5/8

F = 42.5 N

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