PHYSICS 1111-D Motion

PRACTICE “CLICKER”If the average velocity is non-zero over some time interval, does this mean that the instantaneous velocity in never zero during the same interval?

1. Yes2. no

ANSWER: NO Your instantaneous can 0 or negative for a time, but the average can still be zero

Example: 6+2+9+0 (meters) / 4sec = 4.25

A CAR GOES FROM 20 MI/HR TO 50 MI/HR WITH AN ACCELERATION OF 4.2. HOW LONG DOES IT TAKE TO REACH THIS SPEED?

What is given and what do we need to find?

How do we decide what equation to use?

ANSWER: V final = v initial + a(t)

Vf= 50Vi=20A= 4.2WANT t =???

50 = 20 + 4.2(t)T= 7.1 seconds

TRIG REVIEW Soh-Cah-Toa

PRACTICE PROBLEM: Fred is practicing shooting at the range.

Fred is standing 50 meters away from his target. When Fred shoots at an angle of 10 degrees, he hits the bottom of the target, but then when he shots at an angle of 4 degrees, he hits the top of the target. At what angle does he have to shoot to hit the middle of the target, if the target is a square.

(HINT: Draw a picture)

ANSWER: Find the height of both shots

Subtract them to get the height of the target

Divide in half to get the middle hieghtPlug answer and adjacent back into tan

function to find the angle (Answer and process in previous lecture)

You throw a ball upward with an initial speed of 10 m/s. Assuming that there is no air resistance, what is its speed when it returns to you?

A. More than 10 m/sB. 10 m/sC. Less than 10 m/sD. zero

ANSWER: 10 m/s!!

Since acceleration is gravity and is the same on the way up and down, the ball will return to the same velocity

You drop a rock off of a bridge. When the rock has fallen 4 m, you drop a second rock. As the two rocks continue to fall, what happens to their separation?

a) Separation increases as they fall

b) Separation stay constantc) Separation decreases

ANSWER: The separation increases as they

fallWhy??

They increase at the same acceleration, but do not have the same velocity

The first rock will always have a greater velocity than the second, and the distance in-between will increase

CONSIDER THE FOLLOWING GRAPHS:

You toss a ball straight up in the air and catch it again. What graph represents this?

THE GRAPH THAT GOES FROM POSITIVE TO NEGATIVE IN A STRAIGHT LINE

WITH THE SAME FOUR GRAPHS: You drop a very bouncy ball. It

falls, and then it hits the floor and bounces right back up to you. Which graph represents this?

FINALLY, You drop the ball and it leaves your

hand, but doesn’t hit the floor. What graph is this?

You accidently drop your curly fries while walking to your table. Your fries fall halfway to the group in .7 seconds. How much time do you left to try to save your fries?

ANSWER: Xf=xi+vi(t)+.5(a)(t)^2

Used to find the heightDelta X 1/2= 0(.7)- .5(9.8)(.7)^2X 1/2= height = 2.401 m *2 = 4.8 m

Plug delta Hs into equation 4.8 = 0 - .5(9.8)(t)^2 Ttotal = 1 second

Ttotal = t first half + t second half1-.7 = t second half

=.3 for second half of fall (Can’t use 2.4 for the X initial because we don’t

know its initial velocity at .7 seconds)

QUESTION: Upton Chuck is riding the Giant Drop at Great America. If Upton free falls for 2.60 seconds, what will be his final velocity and how far will he fall?

ANSWER: Given:

Acceleration Time Initial velocity

Need to find:Distance and Final Velocity

Use: Delta x = Vi*t + .5(9.8)(2.60)^2Distance = 33.1 m

Plug into V final = V initial + a(t)Vfinal = 25.5 m/s

FINAL QUESTION: A bullet is moving at a speed of 367 m/s

when it embeds into a lump of moist clay. The bullet penetrates for a distance of 0.0621 m. Determine the acceleration of the bullet while moving into the clay. (Assume a uniform acceleration.)

ANSWER: Given: vi = 367 m/s vf = 0 m/s d = 0.0621 m

Find acceleration

Use: vf2 = vi

2 + 2*a*d(0 m/s)2 = (367 m/s)2 + 2*(a)*(0.0621 m)A= -1.08*10^6 m/s^2(- means deacceleration, slowing down)