LINEAR MOTIONReview

What is it called when the speed of an objects changes?

ACCELERATION

What’s the difference between speed and velocity?

Speed is how fast an object moves and velocity is speed in a given direction.

What is the speed of a car that traveled 125 miles in 2 hours?

Hint: Make sure you include units! Do NOT ROUND!

d = 125 miles t = 2 hours v = ?

v = d/t v = 125 miles/2

hours v = 62.5 mi/hr

OR 62.5 mph

How much time does it take for a bird flying at a speed of 45 mph to travel a distance of 1800 miles?

Hint: Calculate time in minutes

v = 45 mi/hr d = 1800 miles t = ?

V = d/t t = d/v t = 1800 miles/45

mph t = 40 hours

t = 40 hr *(60min/1 hr) = 2400 min

What is the acceleration due to gravity = to?

g = 9.8 m/s2 ≈ 10 m/s2

_______________ speed is speed at any moment.

Hint: The speedometer in a car measures this.

INSTANTANEOUS

A car accelerates from 25 km/hr to 55 km/hr in 30 minutes. What is its acceleration?

Hint: Make sure your units are km/hr2

vi = 25 km/hr vf = 55 km/hr t = 30 min a = ?

a = (vf – vi)/t a = (55 -25)/0.5 hr a = 60 km/hr2

Is the velocity of this object constant or changing? What is the velocity?

s

Constant Velocity Slope = rise/run =Δy/Δx

Slope = dist/time Slope = (50-0)/(5-

0) Slope = 10 m/s

What do we mean when we say motion is relative?

It is measured with respect to something

A train is accelerating at a rate of 2 m/s2. If its initial velocity is 20 m/s, what is its velocity after 30 seconds?

a = 2 m/s2 vi = 20 m/s t = 30 sec vf = ?

a = (vf – vi)/t 2 = (vf – 20)/30 30*2 = vf – 20 60 = vf – 20 80 m/s = vf

What is the motion of this object?

Object is NOT moving or it is at rest.

Is acceleration occurring according to this graph?

Yes the speed is increasing at the same rate; this is why it’s linear.

True or False.

On the Moon, ALL objects accelerate at the same rate.

TRUE. No air exists on the moon, therefore there is no resistance pushing against the force of gravity.

Draw the path of an object being thrown up and coming back down (free fall). Show what happens to speed when: It’s going up At the top Coming back down

Suppose that a ball is dropped from a tower 70.0m high. How far will it have fallen after 1.00 s, 2.00 s, and 3.00 s? Neglect air resistance.

g = 10 m/s2

t = 1 s, 2 s, 3 s d = ½ *g*t2

d = ½ * 10 m/s2* (1 s)2

d = 5 m/s2 * 1 s2

d = 5 m d = ½ * 10 m/s2*

(2 s)2

d = 5 m/s2 * 4 s2

d = 20 m d = ½ * 10 m/s2*

(3 s)2 d = 5 m/s2 * 9 s2 d = 45 m

Suppose an object is thrown downward with an initial velocity of 3.0 m/s, instead of being dropped. What would its speed be after 1.0 s and 2.0 s?

Hint: Use vf = vi + a*t

vi = 3 m/s t = 1 s, 2 s g = 10 m/s2

vf = ?

vf = vi + a * t vf = 3 m/s +

(10m/s2 * 1 s) vf = 3 m/s + 10

m/s vf = 13 m/s vf = 3 m/s +

(10m/s2 * 2 s) vf = 3 m/s + 20

m/s vf = 23 m/s