12PHYS - Mechanics

Finn LeSueur

2021

- Yssy travels 30km south and then 20km west. Draw a vector diagram to show her total
**displacement (resultant)**. - Max and Lena are pushing a box. Max is pushing it with force 500N to the right, and Lena is pushing it with force 400N up. Draw a vector diagram to show the
**net (resultant) force**. - Phoebe is flying at \(7ms^{-1}\) east. Phoebe changes direction so she flying at \(7ms^{-1}\) south. Draw a vector diagram to show the
**change in velocity**of Phoebe.

- Be able to describe the motion of an object undergoing projectile motion.

Write the date and te whāinga ako in your book

- First, watch this clip and count how many seconds the student was in the air for
- Second, open Google Classroom and find the Projectile Motion whakamātau/experiment.

Motion under gravity.

To get into projectile motion we first need to correctly describe the *velocity* and *acceleration* of an object in motion.

A ball is thrown vertically upwards. **In pairs on a whiteboard, draw a diagram and describe the direction of the ball’s velocity and acceleration when:**

- It is going up,
- it is going down,
- it is at the highest point.

- We assume that friction force is negligible (we ignore it).
- Therefore,
*the only force*acting upon the ball while in the air is the**weight force**.

The ball experiences a constant downwards acceleration (\(-9.8ms^{-2}\)) at all times, and **no** acceleration in the horizontal direction.

The acceleration of any object in the air without its own power source.

Calculate the height that your ball reached yesterday in your experiment

- An object that moves through the air
**without its own power source**, - only force acting upon it is the
**weight force**, - always experiencing
**downward acceleration of \(9.8ms^{-2}\)**, - motion up/down is symmetrical.

A ball is thrown upwards with an initial speed of \(161.3km/hr\) (\(44.8ms^{-1}\)).

- How long does it take for the ball to reach its highest point?
- How high does the ball rise?

**Remember:** Knowns, Unknowns, Formula, Substitute, Solve

Lachie kicks a rugby ball straight upwards. It is in the air for \(10.6s\) before it hits the ground.

- What is the initial velocity of the ball?
- How high does the ball rise?

**Remember:** Knowns, Unknowns, Formula, Substitute, Solve

Angus is going cliff diving. He jumps and falls for \(3.4s\) before hitting the water below.

- What is his
**initial velocity**? - What is his
**acceleration**? - What is his
**final velocity**(as he hits the water)? - How
**high**is the cliff?

**Remember:** Knowns, Unknowns, Formula, Substitute, Solve

- Complete Worksheet 5
- Textbook Activity 8C Q1-6
**Manatu/Remember**: Homework Kinematics Q1 due Tuesday!

A cannon ball is fired horizontally from the top of a hill. The velocity of the cannon ball is split into \(x\) and \(y\) components, which are independent of each other.

**Recall:**once in motion, the only force acting upon the cannon ball is the**weight force**. We are assuming friction is negligible.- Therefore: the cannon ball is experiencing a constant downward acceleration of \(g=-9.8ms^{-2}\).

**Recall:**once in motion, the only force acting upon the cannon ball is the**weight force**. We are assuming friction is negligible.- Therefore, the cannon ball does not experience any forces in the horizontal direction. Therefore it does not accelerate in the horizontal direction.

Constant downwards acceleration of \(-9.8ms^{-2}\).

No acceleration, therefore constant speed. \(v_{i} = v_{f}\)

If the cannon ball is fired with a **greater horizontal velocity** will it take longer to hit the ground?

A marble rolls of a desk of height 1.25m and with \(v_{x} = 1.6ms^{-1}\).

- Calculate the
**duration of the fall**. - During the fall, how far does the marble travel
**horizontally**? - How far does the marble travel if \(v_{x} = 3ms^{-1}\)?