Physics 11 Advanced

Mr. Jean

April 2nd, 2012

The plan:

• Video clip of the day

• Forces & Acceleration

• Applied 2d forces

The rocket: • A 450g rocket experiences 16N of thrust force

in the upwards direction. The force continues for 5 seconds. – A) Draw the force diagram for this situation. – B) What is the rockets acceleration?– C) What is the rockets velocity after the 5

seconds? – D) How fast is the rocket traveling 10 seconds

after the thrust concludes?

Force Diagram:

Acceleration:

Velocity after 5 seconds:

Velocity 10 seconds after thrust:

Second Law Part #2

• http://www.brightstorm.com/science/physics/newtons-laws-of-motion/law-of-force-and-acceleration-newtons-second-law-of-motion/

Forces in two-dimensions:

• A 45kg crate is being pulled eastwards horizontally across the floor. The coefficient of friction is 0.2. You pull the crate with a force of 115 N at an angle of 15 degrees. – A) What is the acceleration?– B) How long does it take the crate to be

moving at 1.4m/s?

2-D Applied Forces:• Step #1: Draw a free body diagram• Step #2: List all of the forces / motions you know.• Step #3: List all of the forces / motions you need to

know.• Step #4: Key assumptions.• Step #5: Determine net forces in vertical direction.• Step #6: Determine net forces in horizontal

direction.• Step #7: Solve for acceleration.

Draw the “Force Diagram”:

Write down the known variables:

Begin to solve the problem:• Find normal force:

• NOTE: We must account for upwards pull by rope. (Fvertical will reduce Fn’s load)

• Fn =

• Ff = is opposing the horizontal acceleration

• Once we find Ff we can then compare the Fnet to determine the horizontal motion.

Find Force of Friction:

V = 1.4m/s when…

Problems to work on:

• P. 171– Question #11 & 12

– Solutions in 20 minutes

Solutions:

Situations 1 of 4

• 1) I am driving on a level surface when I jam my brakes in my 2000kg car. My car is not stopped, but it is coming to a stop. The surface and tires have a coefficient of friction of 0.5.

Situations 2 of 4

• 2) A 2kg brick is being pushed across a level surface at a constant velocity of 4 m/s [W].

Situations 3 of 4

• 3) A 4kg object is thrown off a cliff on the moon at the angle of 45 degrees from the horizontal.

Situations 4 of 4

• 4) A 50kg person is accelerating upwards on an elevator at 1.5m/s2.

P. 171 Mini-Lab: