physics 11 advanced mr. jean april 2 nd, 2012. the plan: video clip of the day forces &...
TRANSCRIPT
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: