Kinematics

Question 1

What is kinematics?

Answer 1

The description of motion in terms of an objects position, velocity, and acceleration.

Question 2

Define displacement.

Answer 2

The displacement of an object is its change in position. Displacement is a vector that always points from the objects initial position to its final, REGARDLESS OF PATH the object took, and whose magnitude is the net distance traveled by the object.

Question 3

The formula for displacement.

Answer 3

d = final position - initial position = net distance plus direction; remeber it’s the shortest path.

Question 4

Define velocity.

Answer 4

Velocity tells us how fast an object’s position changes.

Question 5

True or false. Velocity always points in the same direction as displacement.

Answer 5

True.

Question 6

What is the formula for average velocity?

Answer 6

average velocity = Δx/Δt

Question 7

Define speed.

Answer 7

Speed is the magnitude of the velocity. It is a scalar and has no direction and can never be negative. It is the TOTAL distance/time.

Question 8

Let’s say there are two cars going at the same speed but different directions. One is going straight to the right. One is heading diagonally. Do they have the same velocity?

Answer 8

No. They have different velocities. Velocity is speed and direction.

Question 9

A RBC completes a circuit of 3m in one minute. What is the average velocity and speed of the RBC?

Answer 9

If a circuit is completed, the displacement is 0. By definition, the average v must be 0m/s. Speed is the total distance over the time. So it is 1/20 m/s.

Question 10

Define acceleration.

Answer 10

Accerlation is how fast an object’s velocity is changing.

average acceleration = change in velocity/time

Question 11

Can an object accelerate even if its speed is constant?

Answer 11

Yes. An object’s velocity changes if the speed or the direction changes.

Question 12

If you toss a ball straight up in the air, what is the velocity and acceleration at the very top?

Answer 12

The velocity is 0, when the ball reaches the top of its path. The acceleration depends, but it’s not zero. Zero would mean the velocity is constant and thus the ball is still going. The direction of the ball’s velocity is now pointing down. That is a change in acceleration.

Question 13

If the acceleration points in the same direction as the initial velocity, then the object’s speed is (increasing/decreasing).

Answer 13

Increasing.

Question 14

If the acceleration points in the direction opposite to the initial velocity, then the object’s speed is (increasing/decreasing)?

Answer 14

Decreasing.

Question 15

The velocity of an object moving along a straight line changes from 7m/s at time = 0 to 1m/s, 3 seconds later. What is the acceleration?

Answer 15

-2m/s^2

Question 16

a at an angle between 0 and 90 to v means object’s speed is (increasing/decreasing) and direction of v is changing.

Answer 16

a at an angle between 0 and 90 to v means object’s speed is increasing and direction of v is changing.

Question 17

Write out the big 5 equations.

Answer 17

1) d = 1/2(v0 + v)t, missing a
2) v = v0 + at, missing d
3) d = v0t +1/2at^2, missing v
4) d = vt - 1/2at^2, missing v0
5) v^2 = v0^2 + 2ad, missing t

Question 18

By convention, the direction of the object’s displacement should be taken as the positive direction. 1) If an object is dropped, what is the sign of gravity?
2) If an object is tossed up, what is the sign of gravity?

Answer 18

1) If an object is dropped, going down is positive, and so is gravity. 2) If an object is tossed upward, then gravity should be negative, and going upward is positive.

Question 19

In projectile motion, the only acceleration is…?

Answer 19

The object experiences only the constant, downward acceleration due to gravity (free fall). This is projectile motion.

Question 20

In projectile motion, acceleration in the horizontal direction is ___.

Answer 20

Once the projectile is launched, it no longer experiences a horizontal a. The “a” will be constant throughout the projectile’s flight. Since the a = 0, the horizontal v is also constant throughout the flight.

Question 21

Comment on the horizontal velocity in projectile motion.

Answer 21

The horizontal v doesn’t change. The initial horizontal v at any point during the projectile’s flight will be equal to the initial horizontal v

Question 22

By convention, in projectile motion, up is the ___ direction and down is the ___ direction.

Answer 22

Up is conventionally the positive direction and down is the negative direction. So ay = (-g)

Question 23

Write out the projectile motion equations for displacement, velocity, and acceleration.

Answer 23

Horizontal: x = Vot; Vx = Vox; a o = 0
Vertical: y = Voyt + 0.5(-g)t^2; Vy = Voy + (-g)t; ay = -g

Vox = voCos(theta)
Voy = voSin(theta)

Question 24

True or false. For projectile moving in a parabolic path, it’s only the vertical velocity that’s zero at the top; the horizontal velocity is still there.

Answer 24

True. At the top, Voy = 0.

Question 25

The parabola in projectile motion is symmetrical. What does this say about the time it takes for the object to travel?

Answer 25

The time it takes to reach the to will be the same as the time it takes to drop back down.

Question 26

True or false. If an object is thrown horizontally, it has _____ vertical velocity.

Answer 26

It has NO vertical velocity. So Voy = 0 m/s