Kinematics (Don't know what I did wrong )

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In summary, the car and truck are initially at the same spot at a stop light. When the light turns green, the car begins to accelerate forward at 1.9 meters per second squared while the truck maintains a constant speed of 14 meters per second. After 14.74 seconds, the car catches up to the truck at a distance of 206.4 meters from the intersection. The car's instantaneous velocity at this time is 28 meters per second.
  • #1
BlasterV
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A car is sitting motionless at a stop light. The driver notices a truck in his rear view mirror, coming up in the lane beside the car.

When the light turns green, the car begins to accelerate forward at 1.9 meters per second squared. At exactly the same moment, just as the light turns green, the truck reaches the intersection moving with a constant speed 14 meters per second.

How far is the car from the intersection when it catches up to the truck?
How fast is the car going when it catches up to the truck?

Ok. Let me show my work now:
V = 14m/s, A = 1.9m/s^2

I assumed that in order for the car and truck to be at the same spot, You need to match Distances.

So I did: 14m/s * t = 1/2 (1.9m/s^2) t^2
t = 14.74 seconds.
Plug in, And part 1's answer is 206.4 m
Piece of cake, but then it asks the second part.

I really have no idea the approach.
I know I can't use V = AT ( i.e ) V = 14.74 x 1.9
why? because It asks when it catches up to the truck, which is an instantaneous velocity and not an average velocity.

But I'm stuck here. All I know for part 2 of this problem is the car passes the truck at 14.74s

Any help? Thanks
 
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  • #2
v=at only assumes constant acceleration from zero velocity at t=0. It is instantaneous velocity at time t.
Average velocity would be v= d/t where you know the object was not moving at constant velocity.
 
Last edited:
  • #3
Thanks, Got it easily with that, 28m/s. Thanks again :)
 

What is kinematics?

Kinematics is the branch of physics that studies the motion of objects without considering the forces that cause the motion.

What are the three basic quantities in kinematics?

The three basic quantities in kinematics are displacement, velocity, and acceleration.

What is the difference between speed and velocity?

Speed is a measure of how fast an object is moving, while velocity is a measure of both the speed and direction of an object's motion.

What is the difference between average and instantaneous velocity?

Average velocity is the total displacement of an object over a given time period, while instantaneous velocity is the velocity of an object at a specific moment in time.

What is the difference between distance and displacement?

Distance is the total length of the path traveled by an object, while displacement is the straight-line distance between the starting and ending points of an object's motion.

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