In an emergency braking exercise, a student driver stops a car travelling at 83 km/h [W] in a time of 4.0 s. What is the car's acceleration during this time? (The answer is expressed in units of m/s2.)
a) 5.8 [E]
b) 21 [E]
c) 21 [W]
d) 21 [W]
e) 5.8 [W]
We can use the equation for acceleration:
acceleration = change in velocity / time
First, we need to convert the speed from km/h to m/s:
83 km/h * (1000 m / 1 km) * (1 h / 3600 s) = 23.1 m/s
Now we can calculate the acceleration:
acceleration = (0 m/s - 23.1 m/s) / 4.0 s = -5.8 m/s^2
The negative sign indicates that the acceleration is in the opposite direction of the initial velocity (west in this case). Since we are only interested in the magnitude of the acceleration, we can drop the negative sign.
Therefore, the correct answer is:
e) 5.8 [W]