Unit 2 Assessment Remediation

Unit 2 Assessment Remediation

Projectile Motion - Motion in 2D

Vectors and Scalars

Scalar quantities include MAGNITUDE

Vector quantities include MAGNITUDE and DIRECTION

Check out the examples to the right

Multiple Choice

How do scalars and vectors differ?

• scalers have units

• scalers have direction

• vectors have units

• vectors have direction

Multiple Choice

You are taking a Physics class and hear about a speed that is 35 miles per hour (mph). What is a magnitude and what is the magnitude of 35 mph?

• A numeric value, 35 is the 'amount' and is followed by units of measurement as miles per hour

• A direction, 35 mph identifies a direction, so it is a vector

Adding Vectors

If all of your vectors are in the x direction you can add and subtract them. (same if they were all in the y direction)

If you want to add an x vector to a y vector, you will use Pythagorean theorem.

Example 1

A dog walks 5 m North and then 6m South.

What is its displacement?

Example 2

A dog walks 5 m North and then 6m East.

What is its displacement?

Multiple Choice

In practice B of the figure, which displacement is the horizontal component?

• 30 km, East
• 30 km, West
• 40 km, North
• 40 km, South

Multiple Choice

In practice A of the figure, What is  the magnitude of the  resultant displacement?

• 5 km 
• 8 km
• 11 km
• 15 km

Multiple Choice

If a car moves 12 km North, 19 km East, and 12 km South, what is its displacement?

• 12 km
• 19 km, East
• 31 km
• 43 km, East

Multiple Choice

Bob walks 2 miles north and turns west and walks 2 miles. What is Bob's displacement?

• 4 miles northeast

• 4 miles northeast

• 3 miles northwest

• 3 miles southeast

Multiple Choice

How do you combine vectors if they are at a right angle to each other, and you know two sides?

• Multiply
• Divide
• Pythagorean Theorem
• Use trigonometry

Multiple Choice

What is the resultant of the two vectors shown above?

• +5

• -5

• +15

• -15

Multiple Choice

What is the resultant vector of the two labeled vectors?

• +2 km

• +14 km

• -2 km

• -14 km

Multiple Choice

What is the resultant of these two vectors?

• +17 m

• +3 m

• -17 m

• -3 m

Horizontally Launched Projectiles

A projectile is any object that is in free fall.

A horizontally launched projectile is an object that has an initial horizontal velocity (the blue ball) before it starts to free fall so it will move both horizontally and vertically at the same time.

Multiple Choice

What variable letter is horizontal velocity?

• X
• Y
• V_x
• V_y

Multiple Choice

What variable letter is vertical velocity?

• X
• Y
• V_x
• V_y

Multiple Choice

What is the shape of the path of any projectile?

• Hyperbolic

• Linear

• Parabolic

• Logarithmic

Multiple Choice

Which of the following would NOT be considered a projectile? 

• a cannonball thrown straight up
• a cannon ball rolling down a slope
• a cannonball rolling off a table
• a cannonball thrown in the air

Multiple Choice

Which is another term for an object's vertical displacement?

• Range

• Height

• Trajectory

• Acceleration

Multiple Choice

Which is another term for a projectile's horizontal displacement?

• Range

• Height

• Trajectory

• Acceleration

For all projectiles:

Horizontal velocity remains constant the whole time (look at the v_x value in the animation)

Vertical velocity changes because the force of gravity acts on objects vertically causing them to accelerate at 10 m/s/s down (look at the v_y value in the animation)

X and Y are INDEPENDENT

Calculating Horizontal Projectiles

Split up the horizontal and vertical motion

Only TIME will be the same on each side

Example

A toy car rolls across a table at a constant speed of 3 m/s. The table is 1.2 m tall.

How much time will it take for the car to hit the ground?

What will be the range (horizontal distance) for the car?

Multiple Choice

What can you say about motion in the x and y direction?

• x is dependent on y
• y is dependent on x
• They are dependent on each other.
• They are independent of each other. 

Multiple Choice

What is the horizontal acceleration of a projectile?

• 0 m/s²
• -9.8 m/s²
• -15 m/s²
• - 20 m/s

Multiple Choice

When a ball is projected horizontally, what is its initial vertical velocity?

• 10 m/s
• 0 m/s
• not enough information given
• the velocity given in the problem

Multiple Choice

What is the vertical acceleration of a projectile?

• 0 m/s²

• 10 m/s² down

• 5 m/s² down

• 12 m/s down

Multiple Choice

A ball rolls off of a horizontal table and falls to the ground. The instant the ball leaves the table its vertical velocity is...

• -9.8m/s
• Unknown
• 0m/s
• 9.8m/s

Multiple Choice

As a ball rolls across a table it has a constant horizontal velocity. When the ball rolls off the table the horizontal velocity...

• Stays the same
• Accelerates at -9.8 m/s²
• Accelerates at an unknown value
• Becomes zero

Multiple Choice

As a projectile moves through the air, the motion on y axis is best described as ____,

• free fall acceleration
• uniform motion
• varying speeds
• constant velocity

Multiple Choice

How can you describe the motion on the horizontal axis if you ignore air resistance?

• acceleration due to gravity
• constant velocity
• varying acceleration
• motionless

Multiple Choice

A soccer ball is kicked horizontally off a cliff. What information is needed to find the time to fall?

• The height of the cliff

• The initial speed of the ball

• The mass of the ball

• All of these

Multiple Choice

A cannon is fired horizontally from a 5.0 m tall tower. How much time will it take until the projectile hits the ground?

• 0.5 s

• 1.0 s

• 2.0 s

• 5.0 s

Multiple Choice

A cannonball is launched horizontally at 50 m/s from an 80 m tall cliff. How much time will it take to hit the ground?

• 16 s

• 5 s

• 4 s

• 3 s

Multiple Choice

A cannonball is launched horizontally at 50 m/s from an 80 m tall cliff. How far will it go (horizontally) before hitting the ground?

• 100 m

• 200 m

• 400 m

• 800 m