A car moves with a velocity of 72km/hr. It is brought to rest in 10 secs. Find (1) the velocity in m/s (2) the retardation?

RiverHeights

2 years ago

1) To convert km/hr to m/s is pretty simple
72km/hr can also be written as 72 * 1km/hr
1 km = 1000m
1 hour = 60 * 60 = 3,600s
Now we can just substituse the values
72 * 1000m/3600s
72,000m/3600s
= 20m/s

2) Calculating retardation is the same as calculating acceleration (A)
A = (v-u)/t
V = Final Velocity
U = Inititial Velocity
T = Time

Since we end up at rest, 0m/s will be our final velocity, and 20m/s will be our initial velocity. This all happened in 10 seconds, so our time is 10s. Now we just plug them into our formula

A = (0-20)/10
A = -20/10
A = -2m/s²

Since we were asked for retardation, we don't have to include the - sign
Retardation = 2m/s²