May the Force be with you
A chair is stationary on a slightly angled hill. A student observes that the Normal force and The force of Gravity in this case are 3rd law pairs. Are they correct?
NO! The third law pairs are = Fn (from ground to chair, and chair to ground) and Fg (from earth to chair and chair to earth)
A hollow sphere and a solid sphere roll down a hill. Which one will reach the bottom first?
IDEA: Check out that "spin-ability" AKA rotational inertia
Solid sphere - easier to spin, down the hill faster
A 40 kg box slides down a 5 meter hill. As it falls to a height of 1 meter what is its velocity?
IDEA: Energy is conserved! Use an LOL and your set
8.85 m/s
A tennis ball is shot at 45 degrees with a velocity of 3m/s. How fast is it acceleration horizontally?
0! The horizontal motion of projectiles is independent of it's vertical motion!
A kitchen sink is dropped onto a hard surface and shatters. If the kitchen sink were dropped onto a pillow instead, the sink would survive. What specifically changed between those two situations to allow the sink to survive?
The time was lengthened, which reduced the force (impulse-momentum theorem)
A skateboarder is moving at a constant velocity to the east when the hit a rough surface. What direction must another force be applied to keep him at a constant velocity?
BALANCED FORCES = CONSTANT VELOCITY, so..another force to the east with the same magnitude
A yoyo is spinning in a horizontal circle on a table. The string suddenly gets cut. What direction will the yoyo go?
Tangentially to the circle at that point (There is no longer and centripetal force to keep it spinning)
A clumsy 80kg classmate backs up at 4 m/s and hits a stationary desk on wheels. If the 20 desk and the classmate move together after they collide how fast would they be moving?
Conservation of Momentum! Make an initial and final side and solve like a champ!
Velocity: 3.2 m/s
A box is moving at 1.2 m/s when suddenly a 10 N force is applied to the object pointing west, and another 10 N of force is applied moving east. Which way will it accelerate?
It won't.
IDEA: Balanced Systems = No acceleration
A satellite is in orbit around a planet. How will doubling the mass of the satellite affect its period?
It won’t (key concept: Newton’s Law of Universal Gravitation)
A dad pushes his son on a wagon. The dad exerts 43 N on the wagon, how much force acts on the dad from the wagon?
43! Ever action has an EQUAL AND OPPOSITE FORCE
A student is at the top of a ferris wheel. Determine an equation for the Normal force acting on the student - and write/show it's direction
IDEA: CENTRIPETAL MOTION must have a force that move towards the center
Fn = Fg - Fnet
A block slides down a 1m high hill from rest. At the bottom of the hill it hits and sticks to an identical block. How fast are the two blocks moving together?
2.2 m/s - Conservation of energy to conservation of momentum
A soccer ball is kicked straight up into the air. When the soccer ball is at its peak, is it accelerating?
Yup (key concept: there is still a net force acting downward on the soccer ball)
A mass-spring system oscillates back and forth once every 2 seconds. The spring is replaced and now the system oscillates once every 3 seconds. Did the spring constant increase or decrease?
Decrease (key concept: ratio problems)
Where and in what direction must you place two forces of equal magnitude on a seesaw to result in the greatest angular acceleration? Where would you put them to create the least?
Most: Both push clockwise or counterclockwise and at the ends of the see saw
Least: Both at pivot point
IDEA: Torque: force x distance
A ballerina is spinning at 5 rev/sec for 3 seconds when she opens her arms. Draw a graph of her angular velocity as she spins.
*Graph drawn on board* Idea: conservation of angular momentum
A 5 block is moving at 3 m/s across a smooth surface when it suddenly hits a stretch of some rough ground, after the patch it is moving at 1.1 m/s. What is the magnitude of force the ground applied on the block if it was sliding on the rough surface for 0.4 seconds?
23.75 N (Change in momentum = Impulse, Impulse = force times time)
An elevator has a velocity directed downward as it slows down. Which way, if any, is the direction of the acceleration of the elevator?
Upward acceleration (key concept: unbalanced forces with a net force pointing upward)
A pendulum on Earth has a period of 2 seconds. If that same pendulum were to be moved to the moon, what would you have to change about the pendulum to maintain the same period?
The length of the string would have to be shortened (key concept: ratio problems)
A ball is at rest. How/where should you push the ball to make it spin the fastest? How should you push the ball so it does not spin at all?
Torque = F*d*sin (angle)
push at the edge 90 degrees to cause the greatest spin, push straight on to cause not spin
A 0.5 meter disk is spinning at 4 rev/s when a non-spinning smaller disk is dropped on top. Is angular momentum conserved and is rotational kinetic energy conserved?
Angular momentum YES! Angular KE NO!
Etherm created - angular KE
Momentum no force stopping the motion
A car is driving at a constant speed through a circular track. Is the car accelerating?
Yes, the car is accelerating towards the center of the circle (key concept centripetal force)
A tow truck begins pulling a 100 kg block from rest with increasing tension. The tension after 8 seconds is 100 N. Calculate the velocity of the block after the 8 seconds.
4 m/s (work / area under the curve)