A truck covers 40.0 m in 7.15 s while uniformly slowing down to a velocity of 2.

Question

A truck covers 40.0 m in 7.15 s while uniformly slowing down to a velocity of 2.45 m/s. Find the truck's original speed. m/s2 Find its acceleration. m/s2 In a test run, a certain car accelerates uniformly from zero to 20.2 m/s? s will doubling the time always double the change in speed? yes No why? A train 300 m long is moving on a straight track with a speed of 84.1 km/h. The engineer applies the brakes at a crossing, and later the last car passes the crossing with a speed of 15.9 km/h. Assuming constant acceleration, determine how long the train blocked the crossing. Disregard the width of the crossing. s

Explanation / Answer

9. s= ut+ (1/2) at2. so, 40 = 2.45 x 7.15 + a x 7.15 x 7.15/2 , so a = 0.88 m/s2. since the body is decelarating, a = -0.88 m/s2

v=u+at = 2.45+0.88x7.15 = 8.74 m/s

10. v=u+at , so a = (v-u)/t = 20.2/2.95 = 6.85 m/s2

t = (v-u)/a = 10.1/6.85 = 1.47 s

c. Yes, change in speed (v-u) is directly proportional to time period provided the accelaration is uniform.

11. v2-u2 = 2as. a = (v2-u2)/2s = 0.88 m/s2. convert velocities to m/sbu multiplying them with 5/18.

t=(v-u)/a = 21.6 s

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