Question

if an automobile moving with a velocity of 40 km/h along a straight road brakes uniformly to rest in 5.0 s, by how much must the automobile velocity change each second?(answer should be in m/s)

Answer 1

Explanation:

40kmph=40×5/18=100/9m/s

acceleration=(0-100/9)/5

=>20/9m/s²

=> for each second, 20/9m/s of velocity is decreasing

Answer 2

Answer:

The automobile changes its velocity -2.2 m/s in each second.

Explanation:

The initial velocity of the automobile = u = 40 km/hr

To convert km/hr unit into m/s unit, we have to multiply it by $\frac{5}{18}$ as 1kilometer = 1000m and 1 hr = 3600 second.

u = 40 km/hr = 40 × $\frac{5}{18}$ m/s = $\frac{100}{9}$ m/s

time = t = 5 s.

Final velocity = v = 0.

• Change in velocity in each second is called acceleration. So here we have to calculate the acceleration.
• Acceleration = $\frac{final velocity - initial velocity}{time}$ = $\frac{0 - \frac{100}{9} }{5}$ = $-\frac{20}{9}$ m/s² = - 2.2 m/s²

    The automobile changes its velocity -2.2 m/s in each second.

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