Question

The speed of a car is decreased uniformly from 30. meters per second to 10. meters per second in 4.0 seconds. What was the car's acceleration ?

Answer 1

Hello!

The speed of a car is decreased uniformly from 30. meters per second to 10. meters per second in 4.0 seconds. What was the car's acceleration ?

We have the following data:

V (final velocity) = 10 m/s

Vo (initial velocity) = 30 m/s

ΔV  (speed interval)  = V - Vo → ΔV  = 10 - 30 → ΔV  = - 20 m/s

ΔT (time interval) = 4.0 seconds

a (average acceleration) = ? (in m/s²)

Formula:

$\boxed{a = \dfrac{\Delta{V}}{\Delta{T}}}$

Solving:

$a = \dfrac{\Delta{V}}{\Delta{T}}$

$a = \dfrac{-20\:\dfrac{m}{s}}{4.0\:s}$

$\boxed{\boxed{a = - 5\:\frac{m}{s^2}}}\:\:\:\:\:\:\bf\green{\checkmark}$

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Answer 2

Acceleration (magnitude anyway) = (change in speed) / (time for the change) .

Change in speed = (10 - 30) = -20 m/s

Time for the change = 4.0sec

Magnitude of acceleration = -20/4  =  -5 m/s²