Question

two telegraph poles "A" and "B" at the side of railway are 50m apart.a train which has a uniform acceleration passes pole "A" at speed of 70km/h,and passes "B" 2s later.what is the acceleration of the train ,and how fast is it moving as it passes pole "B"?

Answer 1

(a)

$$s=v_i t+\frac{at^2}{2} \\ 50=19.4\times 2+\frac{a\times 2^2}{2} \\ a=5.6 \;\rm{m/s^2}$$

(b)

$$v_f=v_i+at=19.4+5.6\times 2=31 \;\rm{m/s}$$