Kinematics Review

Match each term with its formal physics definition

• A quantity with a magnitude and a direction

• Vector

• The position of an object relative to its starting location

• Displacement

• A quantity with magnitude, but no direction

• Velocity

• The rate of change of displacement

• Acceleration

• The rate of change of velocity

• Scalar

At the top of a projectile's path, its vertical velocity is:

• Positive

• Zero

• Negative

Answer explanation

If it were positive, it'd still be going up (so not the top), and if it were negative, it'd have already come down!

Alternatively, the projectile has to switch from going up (positive velocity) to going down (negative velocity) by passing through zero.

A cat starts running across the room. She starts from rest, and reaches her top speed of 12 m/s in 0.4 seconds. What is the cat's acceleration? [include units; write seconds squared as s2]

Answer explanation

Use: a = delta v / t

a = 12 m/s / 0.4s

a = 30 m/s2

Tags

NGSS.HS-PS2-1

An object starts its motion at rest. This means that its initial velocity is:

Usain Bolt's world record is 100m in 9.69 seconds, set at the Beijing Olympics. What was his average velocity while running this race? [Round to two decimal places, include units]

A car pulls onto the highway. It accelerates at 2 m/s2, merges over a distance of 100 m, and ends with a velocity of 28 m/s. What was its initial velocity? (Round to two decimal places and use correct units.)

Tags

NGSS.HS-PS2-1

On the d vs t graph below, circle areas of positive acceleration in green, zero acceleration in yellow, and negative acceleration in red

Answer explanation

Curving up - positive a

Straight line - zero a

Curving down - negative a

Tags

NGSS.HS-PS2-1

Suppose I want to determine my cat's acceleration. What experiment could I run to find this out? Describe (briefly) what I would do, what data I should collect, and how I could use that data to calculate her acceleration.

Attach a sketch if desired.

Answer explanation

Your answer should include:

• - measurement of cat's starting velocity (or starts from 0)

• - some way to start the cat moving

• - measurement of time or distance

• - measurement of cat's final velocity

• -using either vf = vi + a t OR vf^2 = vi^2 + 2 a*d to determine a

Tags

NGSS.HS-PS2-1

A projectile is launched with an initial velocity of 10 m/s at an angle of 40 degrees above the horizontal. What is its initial y-velocity? (Round to two decimal places, include units)

A projectile is launched with an initial vertical velocity (y-component) of 6 m/s. How long will it take to hit the ground? (Use g=9.81 m/s2, round your answer to 2 decimals, and include units)

Answer explanation

Use:

dy=vy*t+(1/2)*ay*t^2

dy = 0 (hits the ground level)

ay = -9.81 m/s2

vy = 6 m/s

Algebra:

- divide by t

- move (1/2 * ay* t to other side

- divide by 1/2 * ay

Tags

NGSS.HS-PS2-4