# PHYSICS

posted by .

A 745i BMW car can brake to a stop in a distance of 122 ft from a speed of 60.0 mi/h. To brake to a stop from a speed of 80.0 mi/h requires a stopping distance of 221 ft. What is the average braking acceleration for the following intervals? Express the answers in mi/h/s and in m/s^2

60 mi/h to rest, 80 mi/h to rest,80 mi/h to 60 mi/h

• PHYSICS -

Vf^2 = Vo^2 + 2ad
0 = Vo^2 + 2ad
At 60 mph:
V^2 = -2ad => a = -V^2/2d
a = (60.0 mi/h)^2 / (2)(0.0231mi)
a = -77901.64 mi/h^2
1 mi/h^2 = 3600 mi/(h*s) (why?)
1 mi/(h*s) = 1609m/(3600s)(1s) = 0.447 m/s^2
a = -21.64 mi/h/s = -9.67 m/s^2
You calculate the acceleration when Vo = 80 mph in a similar fashion.

## Similar Questions

1. ### physics

I had wrote that was because I was told that in the beginning of the spring being wound the PE=KE. Can I check a concept question, The amount of work required to stop a moving object would be equal to the mass of the object times it …
2. ### Physics

A car with a mass of 890 kg travels at a speed of 20.0 m/s. Seeing that the road ahead is blocked by a rock slide, the driver applies the brakes, stopping the car. The work of stopping the car becomes thermal energy of the car’s …
3. ### physics

A car with a mass of 890 kg travels at a speed of 20.0 m/s. Seeing that the road ahead is blocked by a rock slide, the driver applies the brakes, stopping the car. The work of stopping the car becomes thermal energy of the car’s …
4. ### physics

A car with a mass of 890 kg travels at a speed of 20.0 m/s. Seeing that the road ahead is blocked by a rock slide, the driver applies the brakes, stopping the car. The work of stopping the car becomes thermal energy of the car’s …
5. ### Physics

A car without ABS (antilock brake system) was moving at 16.5 m/s when the driver hit the brake to make a sudden stop. The coefficients of static and kinetic friction between the tires and the road are 0.553 and 0.410, respectively. …
6. ### Physics

An automobile travelling with a speed of 60km/hr, can apply brake to stop within a distance of 20m. If the car is going twice as fast then calculate the stopping distance and stopping time?
7. ### Algebra

The distance required for an emergency stop for a car varies directly as the square of the car’s speed. A car traveling at 50 mph requires 140 feet to stop. What is the stopping distance for a car traveling at 30 mph?
8. ### science

the distance a car travels between the time the driver decides to stop the car and the time the driver puts on his brake is called the reaction distance how does the reaction distance change with speed
9. ### math (stats)

For a car traveling 30 mph in normal conditions, the distance required to brake to a stop is normally with a mean of 50 feet and a standard deviation of 8. you are traveling in a area at 30 mph and a car swerves into your path at a …
10. ### physics

a car is moving at speed of 50km/hr ,can be stopped by brake at least at 6 m.If the same car is moving at speed of 100 km/hr ,what is the minimum stopping distance?

More Similar Questions