# Kinematics Part 2

Both the car’s speed and velocity are changing

A car is speeding up as it drives around a circular track on level ground. Which statement about the car’s velocity and speed is accurate?

always changing

A ball is attached to a string and whirled in a circle at constant speed. As it travels in a circle, its acceleration is __________.

Cosine of alpha is equal to delta r sub x over delta r

Consider a two-dimensional (2D) displacement vector in the x-y plane, with magnitude Delta r and angle Alpha measured counterclockwise from the positive x-axis. Which of these is a correct trigonometric relationship between Delta r, Alpha, Delta r sub x and Delta r sub y?

North of East

A car is driving around a circular track on level ground speeding up as it goes. At a particular moment the car is at the westernmost point on the track, heading north. What direction is the car’s acceleration at this moment?

can be found using either v times sine theta or v times cosine theta, depending on how theta is measured

Consider a two-dimensional (2D) velocity vector in the x-y plane, Vector v. The x-component of Vector v __________.

The bullet fired from the gun and the dropped bullet have the same acceleration while they are in flight.

In an airless test-facility, a bullet is fired from a gun horizontally, at a height of 1 m. At the same time, another identical bullet is dropped from the same height. What is true about the acceleration of the two bullets while they are in flight?

tangent of theta is equal to a sub y over a sub x

Consider a two-dimensional (2D) acceleration vector in the x-y plane, with magnitude a and angle theta measured counterclockwise from the positive x-axis. Which of these is a correct trigonometric relationship between a, theta, ax and ay?

The car’s velocity points due north.

A car is driving around a circular track on level ground speeding up as it goes. At a particular moment the car is at the westernmost point on the track, heading north. Which statement is correct about the car’s velocity at this moment?

1D vectors have a direction indicated by either a (+) or (-) sign, but 2D vectors have a more complex direction.

Which of these is a key difference between one-dimensional (1D) and two-dimensional (2D) vectors?

The car’s speed is constant, but the velocity is changing.

A car is driving at a steady 15 m/s around a circular track on level ground. Which statement about the car’s velocity and speed is accurate?

A parabolic path

What shape is the path that all objects in projectile motion follow?

The average velocity for some time period equals the object’s displacement during that period divided by that period of time.

As an object moves in the x-y plane, which statement is true about the object’s average velocity?

The bullet fired from the gun will have a greater impact velocity than the dropped bullet.

A bullet is fired from a gun horizontally, at a height of 1 m. At the same time, another identical bullet is dropped from the same height. What is true about the impact velocities (or final velocities) of these two bullets?

The velocity at the top is equal to the x-component of the initial velocity.

A basketball is moving in projectile motion. What can you say about the ball’s velocity at the top of its trajectory?

zero

The horizontal component of the acceleration of an object experiencing projectile motion is __________.

will increase in magnitude

A ball is attached to a string and whirled in a circle at constant speed. If we swing the ball so that it goes around the circle more often, its acceleration __________.

The ball’s speed is the same as when it was tossed, but its velocity is different.

During volleyball practice a volleyball is tossed over a net, starting from a height of 1.5 meters above the ground. After flying over the net it returns to that height as it falls. What is true about the ball’s motion at that moment?

The puck’s acceleration must have a component that points to the east.

Imagine a hockey puck sliding northward on an ice rink. In order for the puck’s path to curve toward the east, what must be true about its acceleration?

The horizontal velocity won’t necessarily be affected if the initial vertical velocity increases.

If you increase the initial vertical velocity of a projectile what happens to its horizontal velocity?

downward

The vertical component of the acceleration of an object experiencing projectile motion is ___________.

The ball’s acceleration is the same at the two moments, but its velocity is different.

During volleyball practice a volleyball is tossed over a net, starting from a height of 1.5 meters above the ground. After reaching the top of its trajectory it returns to its original height as it falls. How does the motion of the ball at the top of its trajectory compare to its motion as it passes its original height?

stays constant the entire time it is in flight

The horizontal component of the velocity of an object experiencing projectile motion __________.

The car’s change in velocity will be south of west.

A car is driving around a circular track at constant speed. At one instant, the car is driving northward and sometime later the car is driving westward. What is the direction of the car’s average change in velocity during this time interval?

The average acceleration for some period of time equals the change in the object’s velocity during that period divided by the change in time during that period.

As an object moves in the x-y plane, which statement is true about the object’s average acceleration?

the instantaneous velocity is tangent to the object’s path

As an object moves in the x-y plane, which statement is true about the object’s instantaneous velocity at a given moment?