Why is acceleration positive in this exercise?

In summary, to calculate the acceleration of a 1400kg car that can stop from 35km/h on a dime, we use the equation v^2=v0^2+2a(x-x0) and solve for a to get -2779m/s^2. To find the force felt by the 68kg occupant, we use F=ma and plug in the calculated acceleration, resulting in a negative force. However, the book may be looking for the magnitude of the force, which would be positive.
  • #1
Frankenstein19
56
0

Homework Statement


Calculate the acceleration of a 1400kg car if it can stop from 35km/h (9.72m/s) on a dime (diameter= 1.7cm) (0.017m). What is the force felt by the 68kg occupant of the car?

Homework Equations


v^2=v0^2+2a(x-x0)
F=ma

The Attempt at a Solution


ok after solving for a in that equation i get -2779m/s^2. when i go to calculate the force felt by the 68kg constituant, i'd just plug everything in, which would mean i'd get a negative force. the back of my book says that the answer is correct but instead of it being negative like i have it it is positive. WHY? why was the acceleration changed?
 
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  • #2
It's difficult to tell without having the book, but it's likely that it was simply looking for the magnitude of the force, which would be positive.
 
  • #3
axmls said:
It's difficult to tell without having the book, but it's likely that it was simply looking for the magnitude of the force, which would be positive.
Capture.PNG
the books question
Capture2.PNG


the answer
 
  • #4
Yes, it looks like they're just looking for the magnitude of the force.
 

Related to Why is acceleration positive in this exercise?

1. Why is acceleration positive in this exercise?

In this exercise, acceleration is positive because the object is speeding up. This means that its velocity is increasing over time. Acceleration is a vector quantity, meaning it has both magnitude and direction. In this case, the direction of acceleration is the same as the direction of the object's motion, resulting in a positive value.

2. How is acceleration determined to be positive or negative?

The sign of acceleration is determined by the direction of the object's motion. If the object is moving in a positive direction, the acceleration will also be positive. If the object is moving in a negative direction, the acceleration will be negative. This is because acceleration is defined as the rate of change of velocity, and the direction of velocity is taken into account.

3. What is the difference between positive and negative acceleration?

Positive acceleration indicates that the object is speeding up, while negative acceleration (or deceleration) indicates that the object is slowing down. This means that the object's velocity is either increasing or decreasing over time. Another way to think about it is that positive acceleration results in a positive change in velocity, while negative acceleration results in a negative change in velocity.

4. Can acceleration be both positive and negative?

Yes, acceleration can change from positive to negative, or vice versa, depending on the object's motion. For example, when a car is accelerating, its acceleration is positive. However, when the car starts to slow down, its acceleration becomes negative. This is because acceleration is a vector quantity that takes into account both magnitude and direction.

5. How does positive acceleration affect an object's motion?

Positive acceleration causes an object's velocity to increase over time. This means that the object will be moving faster and covering more distance in a given amount of time. The amount of acceleration also affects the rate at which the object's velocity increases. The greater the acceleration, the faster the object's velocity will increase.

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