9.24 Kinematics

Match the measurement with the term.

Groups:

(a) Speed

,

(b) Velocity

,

(c) Acceleration

• 10 km/hr^2

• 10 km/hr north

• 6 m/s^2

• 10 km/hr

• 6 m/s

• 6 m/s west

Answer explanation

Speed is a distance per time, like mi/hr. Velocities will look like speeds but have a direction with them, like mi/hr east.

Accelerations will have the time unit squared. If exponents aren't available, we use a ^ to denote the exponent.

Match the term with the definition.

• distance per unit time

• Velocity

• change in velocity per unit time

• Acceleration

• Speed in a given direction

• Magnitude

• Amount or quantity

• Speed

• magnitude with a direction

• Vector

Tags

NGSS.MS-PS3-1

A ball rolls 15 meters in 3 seconds. What was its speed?

• 5

• 5 m/s

• 5 mph

• 45 m/s

• 0.2 m/s

Answer explanation

Remember, speed is distance divided by time.

Distances are measured in units like meters (m), miles (mi), kilometers (km), centimeters (cm), and millimeters (mm).

Times are measured in units like seconds (s), minutes (min), and hours (hr).

A car is traveling at 20 m/s when the driver hits the brakes. The car comes to a stop in 2 s. What was the acceleration of the car?

• 10 m/s²

• -10 m/s²

• 40 m/s²

• -40 m/s²

Answer explanation

Acceleration is the change in speed divided by time. The car started at 20 m/s and came to a stop ( 0 m/s). When you subtract final speed - starting speed, you get 0 - 20 = -20. Divided that by the time of 2 seconds, and you get -10. Now look at the units! m/s divided by s gives us m/s².

You can double check the sign of your answer by determining if the object is speeding up or slowing down. If it is speeding up, the answer is positive. If it is slowing down, the answer is negative.

Tags

NGSS.MS-PS2-2

Select all of the ways an object can accelerate.

• Speed up

• Slow down

• Change directions

• Stay at constant speed

• Stay in a constant direction

Answer explanation

Velocity is speed in a given direction.

Acceleration is a change in velocity. So if we change anything about the velocity, the object is accelerating. We could change the speed or the direction to change the velocity. The speed can increase or decrease. The direction can also change to change velocity.

Any of these changes in velocity means the object accelerates.