# I have mass and velocity, how do I get accel?

• knight4life
In summary, the conversation discusses the problem of finding the acceleration and distance traveled of a car when its driver suddenly applies the brakes on a slippery road. The weight of the car is 1750 kg and the friction force between the road and tires is 25% of the weight of the car. The correct way to solve this problem is by using Newton's law, where the friction force is equal to -ma and the acceleration is (-1/4)g m/s^2. The distance traveled can then be found using the equation Vf-Vi=2*a*delta x, where Vf is the final velocity and Vi is the initial velocity, which in this case is zero.
knight4life

## Homework Statement

The driver of a 1750 kg car traveling on a horizontal road at 110 km/h suddenly applies the brakes. Due to a slippery pavement, the friction of the road on the tires of the car, which is what slows down the car, is 25% of the weight of the car.

## Homework Equations

(a) What is the acceleration of the car?

(b) How many meters does it travel before
stopping under these conditions?

## The Attempt at a Solution

I keep getting -2.7m/s^2 and i cannot figure out the correct way to do it.

knight4life said:

## The Attempt at a Solution

I keep getting -2.7m/s^2 and i cannot figure out the correct way to do it.
How did you get that value? (Hint: Use Newton's law.)

Doc Al said:
How did you get that value? (Hint: Use Newton's law.)

I don't know, I cannot seem to get that value again.

For part a, you do not even need the velocity of the truck. If you use Newton's law like Doc Al says, you will have -F(friction)=ma --> F(friction)=-ma, which makes sense because the truck is decelerating. You know the force of friction is (1/4)mg so a should equal (-1/4)g m/s^2. Then to find the distance traveled, use the equation Vf-Vi=2*a*delta x, where Vf is final velocity and Vi is initial velocity. In this case, your final velocity will be zero.

w3390 said:
For part a, you do not even need the velocity of the truck. If you use Newton's law like Doc Al says, you will have -F(friction)=ma --> F(friction)=-ma, which makes sense because the truck is decelerating. You know the force of friction is (1/4)mg so a should equal (-1/4)g m/s^2.

Thank you very much. I was trying to figure out using kinematics, and getting very angry. I also was assuming that she wanted the acceleration of the vehicle, not that of the friction force.

That is the acceleration of the vehicle. The friction force is used because it is the only force acting on the truck.

## 1. What is acceleration?

Acceleration is the rate of change of an object's velocity. It is the measure of how quickly an object's speed is increasing or decreasing.

## 2. How is acceleration calculated?

Acceleration is calculated by dividing the change in velocity by the change in time. The formula for acceleration is a = (vf - vi)/t, where a is acceleration, vf is final velocity, vi is initial velocity, and t is time.

## 3. Can an object have acceleration without changing its speed?

Yes, an object can have acceleration without changing its speed. This is because acceleration also takes into account changes in direction. For example, an object moving in a circular motion at a constant speed will have acceleration due to its constantly changing direction.

## 4. How do mass and velocity affect acceleration?

Mass and velocity both play a role in determining the acceleration of an object. Generally, the greater the mass of an object, the more force will be needed to accelerate it. Similarly, the greater the velocity of an object, the more force will be needed to change its direction or speed.

## 5. What is the relationship between force and acceleration?

According to Newton's second law of motion, the acceleration of an object is directly proportional to the net force acting on the object and inversely proportional to its mass. This means that a greater force will result in a greater acceleration, while a larger mass will result in a smaller acceleration.

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