9/12 Free Fall, Projectile Motion

Today: examples one new equation HW “9/12 Stunt Man” Due Monday, 9/16

On web or in 213 Witmer for copying

HW 9/11 “Projectile” Due Friday, 9/13On web or in 213 Witmer for copying

Last years practice exam on web and in 213 Exam 1 Thursday 9/19 5-7 pm Wit 116 and 114

Find the Displacement

v (m/s)

t (s)

At what time is the object back where it started from?10

10

What is its velocity at this time?

If it returns to its starting point it must turn around. At what time does it do that?-10

10s

6s

-8m/s

What is the displacement from 2s to 13s?

How many meters were put on the odometer from 2s to 13s?

Projectile Motion Example:An object is thrown with a velocity of 4m/s up and 3m/s west. The acceleration is 10m/s2 directed down.

How long is the object in the air?

How high does it get?

What is its velocity when it gets back to the ground? (Well, impact speed, not at rest.)

4 to 4 is a of 8 of 10 every sec. t = 0.8 seconds

vave,y = 2m/s t = 0.4 to top

Same speed, same angle but below axis now

4m/s3m/s

5m/s @ 53

Example 9 page 41 in text

From rest a motorcycle accelerates at 2.6m/s/s for a distance of 120m. How long did it take? How fast is it going?

Text uses vi2 = vf

2 + 2ax

but fails to say how we multiply vectors.

This equation is off limits for us for this and other reasons but I will give you one to use in these cases.

Combine v/ t = a and x/ t = vave with either vi or vf = 0…...

Get: t = 2 xa

Now you can work out t, v, and vf.

Projectile Motion Example:An object is thrown with a velocity of 4m/s up and 3m/s west. The acceleration is 10m/s2 directed down.

Find the velocity at the point shown, 0/.4m above the ground.

0.4m

Last example we knew the final velocity by symmetry. Now we don’t

tangent

Split the motion into two parts, before the highest point and after the highest point.

Projectile Motion Example:An object is thrown with an unknown velocity at 53 above the horizontal, reaching a height of 6.0m. The acceleration is 10m/s2 directed down.

Find the initial velocity.

6.0m

Split the motion into two parts, before the highest point and after the highest point.