U4 Motion&Force Overview

An airplane averages 350 mi/hr on a 3 hr flight. How far has it gone?

• 350 mi

• 116.7 mi

• 1050 mi

• not enough info

Answer explanation

since s = d/t then d = s * t The average speed * time gives you the distance.

When will speed and velocity have the same value for a moving object?

• They are always the same

• When displacement and distance are equal for the time interval considered

• When distance and displacement are different

• Speed and velocity can't be the same

Answer explanation

s = dist/t while v = disp/t

if distance (dist) and displacement (disp) are the same, then speed and velocity will be equal. This will be true unless an object changes direction during the time considered.

A child is holding a ball in their hand. They throw the ball upward, hitting the ceiling 7ft above their hand... then the ball drops to the floor, 2ft below the child's hand.

• Distance and displacement of the ball are equal

• The ball has a distance traveled of 7ft

• The ball has a displacement of 7ft

• The ball has a displacement of -2ft

Answer explanation

From the hand, the ball goes up 7 and then down 9. This is a distance of 16ft, but a displacement of -2ft.

Tags

NGSS.MS-PS2-4

A car is traveling at 25 m/s when the driver hits the brakes, slowing the car to 15 m/s over a 2.0 second span of time. The acceleration of the car is...

• -10 m/s

• -12.5 m/s/s

• -7.5 m/s

• -5 m/s/s

Answer explanation

accel = change in vel / time

The velocity changes from 25 m/s to 15 m/s... so thats a change of -10m/s... over a time span of 2 seconds.

-10m/s divided by 2s = -5m/s/s

Tags

NGSS.HS-PS2-1

A runner bursts out of the blocks with an acceleration rate of 6 m/s/s... but that only lasts 1.5 seconds. What speed will the runner achieve?

• 6 m/s

• 9 m/s

• 4 m/s

Answer explanation

since a = change in vel / time

change in vel = a * t

6 m/s/s * 1.5 sec = 9 m/s

Since the runner starts at rest, a change of 9 m/s means they achieve a 9m/s speed.

Tags

NGSS.HS-PS2-1

You're riding in a car traveling at highway speeds when the driver hits the brakes. You feel slammed forward against the seatbelt because....

• Mass resists motion

• Your mass wants to maintain its current velocity

• Force from the moving car is pushing you forward into the seatbelt

• Action forces have reaction forces

Answer explanation

inertia!... "mass resists acceleration"

Your body's mass wants to maintain its current velocity... the car slows so you feel pressed forward into the seatbelt... but its actually the seatbelt trying to slow you down.

Tags

NGSS.HS-PS2-1

A 6kg bowling ball is placed on an incline and released. Due to the angle of the incline, it accelerates along the incline at 2 m/s/s. How much force is accelerating the ball down the ramp?

• 12 N

• 6 kg

• 3 N

• 9.8 m/s/s

Answer explanation

F = m*a and... force causes acceleration in the direction of the force. Since the 6kg is accelerating at 2 m/s/s down the ramp, the force down the ramp is 12 N.

Tags

NGSS.HS-PS2-1

In a boxing match, the blue boxer hits the red boxer, knocking the red boxer backward. Which is true?

• The force applied to the red boxer is the same force returned to the blue boxer

• If the red boxer moves with the punch, lengthening the contact time, the force will be less

• The acceleration each person experiences would depend on their mass since the force is the same on both.

• All of these are true

Tags

NGSS.HS-PS2-1

NGSS.HS-PS2-2

If you dropped an object off a tall cliff...

• It will travel 9.8 m farther down for every second it falls

• It will have a speed that increases by 9.8 m/s for every second it falls

• Its acceleration will change by 9.8 m/s/s for every second it falls

• The force on the object will change by 9.8 N for every second it falls

Answer explanation

Objects on earth have a free-fall acceleration of 9.8m/s/s

That means every second the velocity and/or speed changes by 9.8m/s.

Tags

NGSS.HS-PS2-1

Which scenario would have the greatest gravitational force between the objects?

• Two 100,000kg objects that are 20m apart

• Two 50,000kg objects that are 20m apart

• Two 100,000kg objects that are 40m apart

• Two 50,000kg objects that are 40m apart

Answer explanation

Due to the U.Grav. equation, we know that mass directly affects gravitational force and distance inversely affects gravitational force. More mass = more force.

More distance = less force.

Tags

NGSS.HS-PS2-4