Motion & Energy
What do we call the total amount of kinetic energy plus potential energy that an object has?
Mechanical energy = sum of kinetic energy and potential energy.
Which example shows kinetic energy because the object is moving through the air?
Wind blowing (moving air) is an example of kinetic energy.
Which unit from the list below correctly measures distance? (Choose one: meters, Newtons, seconds, or kilograms.)
Correct distance unit: meters (or centimeters are also units of distance
What is the unit used to measure force
Unit of force: Newton.
What property must two objects have for there to be a gravitational force between them?
They must have mass
Give an example from everyday life of an object that has both kinetic energy and potential energy at the same time.
A swinging pendulum near its lowest point has kinetic energy and, because it is above the lowest point, also some potential energy.
Identify the scenario that best represents kinetic energy turning into gravitational potential energy.
A roller coaster climbing toward the top of a rise (moving up) is converting kinetic energy into gravitational potential energy
A boat travels different distances during a 4-hour trip: 68 km in 2 hours, then 3 km in 1 hour, then 25 km in 1 hour. Reword and calculate the boat’s average speed for the whole trip.
Total distance = 68 + 3 + 25 = 96 km. Total time = 4 h. Average speed = total distance / total time = 96 km4 h=24 km/h4 h96 km=24 km/h.
Two objects push on each other during a collision. Restate why the lighter object changes its motion more than the heavier object when both feel the same force
Newton’s second law: same force produces larger acceleration on the object with smaller mass, so the lighter object accelerates more.
Explain why you weigh less on the Moon than on Earth using mass and gravitational force.
The Moon has less mass than Earth, so it exerts a smaller gravitational force — you weigh less.
Name the energy change that happens when an object moves up a slope and slows down because of gravity.
Conversion: kinetic energy is changing into gravitational potential energy as the object climbs.
A satellite orbits Earth at a steady height. Rephrase why it has both kinds of mechanical energy.
The orbiting station has kinetic energy because it’s moving and gravitational potential energy because of its altitude — so it has both.
If a runner runs at 8 km/h for most of a 5-km race but stops briefly, explain why her average speed for the entire race is less than 8 km/h.
Stopping added extra time to her race, so average speed (total distance divided by larger total time) is less than 8 km/h
If one object is pushed and begins to move, explain what must have acted on it in terms of balanced or unbalanced forces.
An unbalanced net force acted on it (net force ≠ 0) causing the change in motion
Define what is true about the forces acting on an object that is in free fall near Earth.
In free fall near Earth (ignoring air resistance), only gravity acts on the object; gravity is the net force causing downward acceleration.
Describe what causes an object that was resting on a hill to begin rolling downhill in terms of forces.
An unbalanced force (component of gravity along the slope) acted on the rock, causing it to move
Explain, in your own words, how the arrangement of objects that interact at a distance can change the amount of stored potential energy
When positions of interacting objects change, potential energy stored in the system changes (e.g., moving masses farther apart changes gravitational potential energy).
An elevator goes 150 ft in a certain time at a speed of 4.5 m/s. Explain what extra information you need to describe its velocity fully.
Need the direction of travel (e.g., up or down) to fully describe velocity
A person applies the same push (100 N) to two balls: one with mass 1 kg and one with mass 2 kg. Reword and explain how their accelerations compare.
Using F=maF=ma, acceleration = 100 N1 kg=100 m/s21 kg100 N=100 m/s2 for the 1-kg ball and 100 N2 kg=50 m/s22 kg100 N=50 m/s2 for the 2-kg ball, so the 1-kg ball accelerates twice as much.
What kind of motion does a net inward (center-directed) force produce? Rephrase with an everyday example.
An inward net force produces curved or circular motion — example: a ball on a string moving in a circle.
Explain why a heavier bowling ball rolling at the same speed as a lighter bowling ball has different mechanical energy
The heavier ball has more mechanical energy when both have the same speed because kinetic energy increases with mass.
Compare how kinetic energy depends on both mass and speed; state which has a bigger effect when doubled.
Kinetic energy depends on mass linearly and on speed squared; doubling speed increases kinetic energy more than doubling mass (doubling speed multiplies KE by 4, doubling mass multiplies KE by 2
Given this speed-time data for a cart: at 0 s speed 0 m/s, at 1 s speed 1 m/s, at 2 s speed 1.9 m/s, at 3 s speed 3 m/s — restate and compute the cart’s average acceleration over the first 3 seconds.
Average acceleration = change in speed / time = (3 m/s − 0 m/s) / 3 s = 1 m/s21 m/s2.
Describe what direction the acceleration vector points compared to the velocity vector when a car brakes abruptly to a stop.
While braking, acceleration vector points opposite to the velocity vector (they are in opposite directions)
Identify which statement below is NOT supported by evidence about gravity:
(A) Gravity depends on masses and distance,
(B) Gravity always pulls objects toward each other,
(C) Gravity depends only on mass and nothing else — restate which is unsupported and explain why.
C. This is not supported because gravitational force also depends on the distance between objects.