Forces
The definition of inertia.
What is...?
measure of mass, tendency of object to resist change in motion.
EX: like a heavy backpack in school that is harder to start or stop moving than a light one.
Unit 1A Answer Key
Which of the following sets of measurements taken by students measuring the length of a classroom table is most precise?
15.01 m, 15.05 m, 15.01 m, 15.03 m
15 m, 17 m, 17 m, 16 m
15 m, 30m, 45 m, 60 m
none of the above
What is...?
15.01 m, 15.05 m, 15.01 m, 15.03 m
EC: Unit 1A Practice Questions
The Law of Conservation of Momentum.
What is...?
Net momentum always remains constant.
EX: In a school hallway collision between two carts, the total momentum before the collision equals the total momentum after the collision.
Newton's Third Law means.
What is...?
interaction pairs experience equal magnitude forces in opposite directions.
EX: Two students pushing against each other in the hallway experience forces that are equal in strength but act in opposite directions.
The difference between a vector and a scalar.
What is...?
scalars only have magnitude like size while vectors have both magnitude and direction like velocity.
EX: like a student’s walking velocity in the hallway, has both magnitude and direction, while a scalar, like how fast the student is walking, has only magnitude.
Unit 1A Answer Key
True/False: Friction always works against motion.
What is...?
True
EX: Friction like shoes on a gym floor always acts opposite to the direction of motion.
EC: Unit 1A Practice Questions
A kicked soccer ball (mass = 0.145 kg) rolling to the right at 30 m/s collides with a goalie’s foot (mass = 0.935 kg) moving to the left at −55 m/s.
True/False: The ball experiences the same change in momentum as the foot, just in the opposite direction.
What is...?
True. Newton's Third Law proves this.
A 0.5 kg backpack is dropped with an initial velocity of −1.5 m/s onto a tile classroom floor. An identical backpack is dropped with the same initial velocity onto a carpeted classroom floor. Which backpack experiences a greater contact force with the floor?
What is...?
The backpack that lands on the tile floor.
Quiz: EC Unit
You are riding a bike to school after the first big storm of the year. On the way to school, the coefficient of friction between your bike tires and the wet pavement is 0.35. In the middle of campus, you ride across a muddy field where the coefficient of friction is 0.15. On the way home, the pavement is dry and the coefficient of friction is 0.70.
How would these different parts of your ride feel and differ from each other?
What is...?
Part 1 lower mew, slippery
Part 2 lowest mew, hard to change directions
Part 3 highest mew, normal road
Unit 1A Video Key
A student walks 15 miles from home to a football game. On the way back home, the student runs out of energy halfway back. What is the student’s displacement?
What is...?
7.5 miles
What is the mass of a library book moving down a classroom table at 3 m/s if its momentum is 0.25 kg·m/s?
What is...?
0.08 kg.
a) A student runs around the school track during PE class. The direction of the student’s acceleration is.
b) A tetherball at recess moves in a circle around the pole. The centripetal force on the tetherball is due to.
What is...?
a) towards the center of the circle/turn.
b) the tension force of the rope.
EC: Unit 2A Practice Questions
A student is pushing a heavy rolling lab cart that has a mass of 750 kg. The student pushes on the cart with a force of 500 N to the left, but the cart does not move.
a) What is the force of static friction on the cart? Show your work using equations.
b) Calculate the force of Earth on the cart and the force of the floor on the cart.
What is...?
a. IN UNIT 1A VIDEO KEY Question 7
b. 500N
Unit 1A Review Sheet
A kicked soccer ball (mass = 0.145 kg) moving to the right at 30 m/s collides with a player’s foot (mass = 0.935 kg) moving to the left at −55 m/s.
True/False: The ball experiences the same force as the foot, just in the opposite direction.
What is...?
True.
EC: Unit 1A Practice Questions AND Unit 1A Review Sheet
A paper wad (m = 5 grams) is thrown at a rolling classroom cart (m = 500 grams) with a velocity of 9.5 m/s. The paper wad bounces back and the cart moves forward. What is the momentum of the paper wad before the collision?
What is...?
P = 0.0475kg*m/s
Unit 2A ReviewSheet
At what velocity would a 5 kg rolling backpack in the hallway have to travel to have the same momentum as a 50 kg student walking at 1 m/s?
What is...?
10 m/s
12. In the Fan Cart Lab you established that the acceleration of an object is dependent on the net forces acting on that object and the mass of that object.
b. How can you find the acceleration on the velocity vs. time graph? On the acceleration vs. time graph?
c. In class, we kept the mass of the cart constant and changed the force applied to measure acceleration. If we then kept the force applied by the fan constant and increased the mass, how would you expect the acceleration to change?
What is...?
b. on a v-t graph acceleration is the slope
on a a-t graph acceleration is the mean value
c. Newton's 2nd Law and net force is proportional to mass and acceleration. This means mass and acceleration are inversely proportional to each other.
Unit 1A Test Review Video Key
A sign in a school elevator states that the maximum occupancy is 20 students. Suppose the safety engineers assume the mass of the average student is 75 kg. The elevator itself has a mass of 500 kg. The cable supporting the elevator can tolerate a maximum force of 30,000 N.
What is the greatest acceleration the elevator’s motor can produce without snapping the supporting cable?
What is...?
5.2m/s^2
Unit 1A Review Sheet
A red hallway cart with a rightward momentum of 0.75 kg·m/s collides with a blue hallway cart moving leftward with a momentum of −0.75 kg·m/s. The two carts stick together and come to a complete stop after the collision.
If the mass of the red cart is 0.25 kg, what was the velocity of the cart before the collision?
What is...?
Velocity could be 0.75 m/s or 3 m/s.
EC: Unit 2A Practice Questions
The school has a circular running track with a radius of 1740 m, and the centripetal acceleration needed at the edge of the track is approximately 1.7 m/s². Assume a remote-controlled cart is driven in a low circular path 50 m farther out from the track.
a) What tangential velocity will the cart need to maintain this circular motion?
b) What is the time it takes the cart to complete one lap?
What is...?
a. v = 1744.42m/s
b. T = 6447.36s
Unit 2A Review Sheet