Exam 1--141 Flashcards
x_final = x_initial + (average velocity)*(delta t)
Explain why x_final is made up of these two parts
multiplying average velocity by delta t should give how far you went in the total time due to your velocity
however, this is not necessarily where you end up. the starting position matters
you need to add x_initial to how far you moved to get where you end up (x_final)
Why can you not just multiple acceleration by time to get velocity and then velocity by time to get distance traveled? The units work out?
This implies that the car is going for one velocity the entire time
The work needs to show that velocity is changing by adding 1/2at^2. Or the student needs to use the average velocity
Why can’t you throw a bowling ball as far as a baseball? Mass doesn’t come into play in kinematic questions?
It is hard to make the bowling ball have the same initial velocity as the baseball. Need to overcome more mass.
The reason kinematic equations don’t include mass is because we are only looking at the object when it is in the air, not before throwing it. We don’t care how hard it was to get to the initial velocity
Will a ball launched at 50m/s spend more time in the air on Earth or on Jupiter? On Jupiter gravity is 22.9 m/s there
The ball spends less time in the air on Jupiter
Once in the air, the ball has to slow to 0m/s and return to the ground. On Jupiter, you lose 22.9m/s of velocity every second where on Earth you only lose 9.8m/s every second. Therefore, the ball will reach 0 and turn around faster on Jupiter than on Earth
How can net force be zero and the object not be at rest?
If the object has no net force, then acceleration equals 0. However, you can still have a 0 acceleration when velocity is constant. This would mean there is no net force on the object (no change in velocity) but the object is not at rest either
How does a=-9.8 m/s2 fit in with Newton’s second law?
Since the only force acting on the object is mg (in the downwards direction) F=-mg=ma. If we divide by the m, we get that a=-9.8. This is in the y-direction.
There is no x component of acceleration in free fall because there is no force acting upon the object in the x and the horiztonal velocity remains constant during the trip
How is velocity encoded on a position versus time graph?
as slope
Why does a bowling ball continue straight after hitting a pin but the pin is knocked down? Does Newton’s 3rd law apply here?
Newton’s 3rd law does apply
The bowling ball does not feel as great of an acceleration because it has a larger mass to mediate the force (F/m=a)
Direction also works out because the pin experiences a positive acceleration to the right as it speeds up from rest
The bowling ball experiences a negative acceleration as its speed is decreased a little
What does the sign of velocity encode?
direction
Can velocity be positive if position graph is always negative?
yes
If accleration is positive does this mean you are speeding up?
No
If acceleration is positive but velocity is negative, you are actually slowing down. Going from bigger negative to zero
If accleration is negative does this mean you are slowing down?
No
If acceleration is negative but velocity is also negative, you are going faster in the other direction. Getting bigger negatives
Why does x_final = x_initial + Vit + 1/2at^2 work?
x_initial is the initial position
Vit is the distance traveled if always stayed at Vi for all the motion
1/2at^2 is the extra distance you go since velocity is changing
So how do a golf ball and lead ball fall at the same rate?
Earth pulls more on the lead ball than on the golf ball
Inertia mediates the motion
Inertia
quantifies how hard it is to change an object’s motion
Why does a ball land right back in a horizontally moving canon that it was launched vertically up from?
although the canon adds y-velocity, the x-velocity stays the same as the cart
x and y velocities are independent. the x velocity was given by the cart
x and y physics evolve simultaneously but separately
