A parking garage ramp winds up three stories, mixing sloped stretches with flat, level turns. Yael's car climbs it from the street to the roof.
Last lesson said the GPE change reads only the height. Why doesn't all that extra winding count?
Take one level turn. The car moves horizontally, and its weight acts straight down, at right angles to the motion.
You saw the reason earlier in this topic: a force perpendicular to the motion has no component parallel to the direction of movement, so it transfers no energy.
So on every level stretch, gravity does zero work on the car. Level stretches cannot change its stored energy.
A level moving walkway carries Vada's 90 N duffel bag 12 m through an airport terminal. Enter the work gravity does on the bag during the level ride, in J.
Now take a sloped stretch. Split the car's movement into two parts: a level part and a vertical rise.
The level part is at right angles to the weight, so it counts for nothing. Only the vertical rise lets gravity do work.
Add up every stretch of the whole winding ramp. All the level parts drop out, and the vertical rises add up to one number: the total height gained.
A hotel luggage cart rolls 9.0 m over a level lobby floor carrying a 180 N suitcase. How much work does gravity do on the suitcase?
The suitcase's motion is horizontal; its weight acts straight down.
The weight is perpendicular to the motion, so it has no component parallel to the movement.
A force with no component parallel to the movement transfers no energy.
Gravity does 0 J of work on the suitcase during the level roll.
A 300 N gear box is dragged up a 10 m ramp whose top is 2.0 m above its base. How much work is done against gravity?
Split the trip: level movement and vertical rise.
Only the 2.0 m vertical rise counts against gravity.
Work against gravity = weight × height gained: 300 × 2.0 = 600.
600 J, the same as lifting the gear box straight up 2.0 m.
On the flat landing halfway up a staircase, a climber's 70 N backpack moves 2.0 m horizontally, and gravity does no work on it there. Why?
Two ropes haul identical 200 N crates up to a 3.0 m loft: one crate straight up, the other up a long 9.0 m ramp. Compare the work done against gravity on the two crates.
A delivery drone flies a package around a city block at a constant height. Which statement about gravity's work on the package during the level flight is right?
A 450 N cart of stage props is rolled 15 m over a level stage floor, then raised 2.0 m on a lift platform. Enter the work done against gravity for the whole move, in J.
A switchback trail climbs 120 m of height over 600 m of path. A hiker carries a 55 N pack to the top. Enter the work done against gravity on the pack, in J.