How Fast Must the Car Travel in the Second Half to Average 51 km/h?

In summary, the conversation discusses the problem of finding the necessary speed for a car to travel during the second half of a 94-km journey in order to average a speed of 51 km/h. The formula for average velocity is mentioned, and the concept of finding the total time for the trip is discussed. The final solution is not the one suggested by Torquescrew.
  • #1
mike5754
3
0

Homework Statement



A car making a 94-km journey travels 39 km/h for the first 47 km. How fast must it go during the second 47 km to average 51 km/h?

Homework Equations





The Attempt at a Solution

 
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  • #2
don't want someone to solve it for me. Just point me in the right direction and help out a little bit.
 
  • #3
Torquescrew said:
Hey, dude. Try using the following formula:
Average Velocity = (Final Velocity + Initial Velocity)/2

Why /2?
I have found that to go 94 km at an average speed of 51 km/h that would be 14.17m/s.
Thus if you went 47 km at 39 km/h you would be moving at 10.83 m/s.
So with this data averaging 51 km/h the entire trip would take 1.52 hours. And the first 47 km (half) would have taken 1 hour. Am I correct so far? So to find the change in time we are looking for it would be 1.52-1.00 giving you .52 hours.

I have Average velocity defined as deltaX/deltaT

deltaX = 47km and delta T = .52 Hours

Thus giving me 90.4 km/h

does this sound right? seems a bit high but maybe I am wrong, this is my first physics class ever. Thanks
 
  • #4
Torquescrew said:
Hey, dude. Try using the following formula:
Average Velocity = (Final Velocity + Initial Velocity)/2

Don't think that's necessarily right. Average velocity is total distance / total time...
 
  • #5
mike5754 said:
Why /2?
I have found that to go 94 km at an average speed of 51 km/h that would be 14.17m/s.
Thus if you went 47 km at 39 km/h you would be moving at 10.83 m/s.
So with this data averaging 51 km/h the entire trip would take 1.52 hours. And the first 47 km (half) would have taken 1 hour. Am I correct so far? So to find the change in time we are looking for it would be 1.52-1.00 giving you .52 hours.

I have Average velocity defined as deltaX/deltaT

deltaX = 47km and delta T = .52 Hours

Thus giving me 90.4 km/h

does this sound right? seems a bit high but maybe I am wrong, this is my first physics class ever. Thanks

I'm not tracking what you are doing. Find t1 = the time to the midway point. Calculate the total time t1+t2 from the total distance and total average velocity. That gives you t2, and you know the distance for the 2nd half of the trip...

(and no, the answer is not what Torquescrew suggested)
 

Related to How Fast Must the Car Travel in the Second Half to Average 51 km/h?

1. What is 1D motion?

1D motion refers to motion that occurs in a single dimension, typically along a straight line. It only takes into account the displacement or change in position of an object, and does not consider any other factors such as velocity or acceleration.

2. How do you calculate displacement in 1D motion?

Displacement in 1D motion is calculated by subtracting the initial position from the final position of an object. This can be represented by the equation: Δx = xf - xi, where Δx is displacement, xf is the final position, and xi is the initial position.

3. What is the difference between distance and displacement in 1D motion?

Distance refers to the total length covered by an object, while displacement refers to the change in position of an object. Distance is a scalar quantity, while displacement is a vector quantity with both magnitude and direction.

4. How does velocity relate to 1D motion?

Velocity is a measurement of an object's speed and direction of motion. In 1D motion, velocity can be calculated by dividing displacement by the time it took to travel that distance. It is represented by the equation: v = Δx / t, where v is velocity, Δx is displacement, and t is time.

5. What is the difference between speed and velocity in 1D motion?

Speed refers to the rate at which an object is moving, while velocity refers to the rate at which an object is changing its position. Speed is a scalar quantity, while velocity is a vector quantity. This means that velocity takes into account the direction of motion, while speed does not.

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