7. A car traveling at a speed of 40.0 is 200 m from a stop sign when the driver

Question

7. A car traveling at a speed of 40.0 is 200 m from a stop sign when the driver realizes he must stop the car at this time. It takes 0.20 s for the driver to apply the brakes. What must the constant acceleration of the car be after the brakes are applied so that the car would come to rest at the stop sign? (a) 2.89 (b) 3.89 (c) 4.17 (d) 3.42 (e) 2.08 8. From what height would a freely falling object need to be dropped to reach a speed of 70.0 before reaching the ground? (a) 250 m (b) 322 m (c) 189 m (d) 500 m (e) 712 m

Explanation / Answer

7)

u = 40 m/s

r = 200 m

t = 0.20 s

distance for stopping , d = 200 - 40 * 0.20

d = 192 m

let the acceleration of the car is a

0 - 40^2 = 2 * a * 192

a = 4.17 m/s^2

the constant acceleration is 4.17 m/s^2

8) let the height is h

v = 70 m/s

h = v^2/(2g)

h = 70^2/(2 * 9.8)

h = 250 m

the height of the falling object is 250 m

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