Rona is driving a car, she travels a 40-90 km/hr and accelerates at 2m/s. How long will take for her to stop the car?

a = (Vf-Vi)/t (where Vf = final velocity and Vi = initial velocity).

So t = (Vf-Vi)/a.

When the car is stopped, the velocity is 0. t=?

Make sure you use the same units.

To determine how long it will take for Rona to stop the car, we need to consider the deceleration of the car.

Given that Rona accelerates at 2 m/s, we can assume that the deceleration when she stops the car is also 2 m/s (assuming no external forces).

We can use the formula for deceleration:

deceleration = (final velocity - initial velocity) / time

Since Rona is trying to stop the car, the final velocity will be 0 km/hr. Let's convert that to m/s:

0 km/hr = 0 m/s

Then, the formula becomes:

2 m/s = (0 m/s - initial velocity) / time

Considering her initial velocity, which is given as 40-90 km/hr, we can find the average initial velocity:

average initial velocity = (40 km/hr + 90 km/hr) / 2

Converting to m/s:

average initial velocity = ((40 km/hr + 90 km/hr) / 2) * (1000 m/1 km) * (1 hr/3600 s)

average initial velocity ≈ 33.33 m/s

Now, let's substitute the known values into the formula:

2 m/s = (0 m/s - 33.33 m/s) / time

To solve for time, let's rearrange the equation:

time = (0 m/s - 33.33 m/s) / 2 m/s

time ≈ -16.67 s

The negative sign indicates that the time calculated here is based on Rona's initial acceleration of 2 m/s. However, if she stops the car abruptly and exerts maximum braking force, the time might differ. It is important to note that abruptly stopping a car is not recommended, as it can be unsafe and cause accidents.