Question

A bus slams on its breaks and goes from 30 km/hr to 15km/hr in 4 seconds. What is its acceleration?

Answer 1

`Formula\ for\ acceleration:\\\\ a=(v_2-v_1)/(t)\\\\ v_1=30km\hr\\v_2=15km\hr\\t=4s\\\\ a=(15-30)/(4)=(-15)/(4)=-3,75(km)/(s^2)\\\\Acceleration\ is\ equal\ to\ 3,75{km}{s^2}. \\Bus\ is\ deccelerating.`

Answer 2

Acceleration is the rate of change of speed.

If the speed is increased then its called acceleration

If the speed is decresed then its a negative acceleration also called deceleration

the formula for calculating acceleration is

`a = (v-u)/(t)`

where a - acceleration

v - final velocity

u - initial velocity

t - time

v - 15 km/hr should be converted to m/s

distance in 1 hour - 15 km

1 hour = 3600 s

1 km - 1000 m

in 3600 s - 15 000 m

in 1 s - 15 000 m / 3600 s = 4.17 m/s

u - 30 km/hr

in 3600 s - 30 000 m

in 1 s - 30 000 m / 3600 s = 8.33 m/s

substituting the values in the equation

`a = (4.17 m/s - 8.33 m/s)/(4 s) = (-4.16)/(4)` = -1.04 m/s²

the answer is negative means its deceleration

the acceleration is -1.04 m/s²