a truck is travelling along a straight road at 72 km/hr.The driver saw a woman crossing and immediately steps on the brake.If the truck stops in 7 sec.what is its acceleration
We will assume that the question is asking for the answer in m s^-2. I would also draw a picture and define the positive direction as the direction of travel. Note that the symbol for time is s not sec.
First convert the velocity km hr^-1 to m s^-1
72 km h^-1 is
72 x 1000 m km^-1 km hr^-1 or
72000 m hr^-1
3600 s hr^-1 so
velocity is
72000 m hr^-1/3600 s hr^-1 =
20 m s^-1
If the truck goes from 20 m s^-1
to 0 m s^-1 in 7 s then the rate of change of velocity (acceleration) is
give by
(final velocity-initial)/t
=(0 m s^-1 - 20 m s^-1)/7 s
=- 20 m s^-1/7 s
To find the acceleration of the truck, we can use the formula:
acceleration = (final velocity - initial velocity) / time
First, let's convert the speed of the truck from km/hr to m/s because the SI unit of acceleration is meters per second squared (m/s^2).
We know that 1 km = 1000 m and 1 hr = 3600 s.
So, the speed of the truck in m/s is:
72 km/hr = (72 * 1000 m) / (3600 s) = 20 m/s
The final velocity is zero because the truck comes to a stop. The initial velocity is 20 m/s, and the time taken to stop is 7 seconds.
Using the formula:
acceleration = (final velocity - initial velocity) / time
acceleration = (0 - 20) m/s / 7 s
acceleration = -20 m/s / 7 s
acceleration ≈ -2.86 m/s^2
Therefore, the acceleration of the truck is approximately -2.86 m/s^2. The negative sign indicates that the truck is decelerating.