When an object moves its length contracts in the direction of motion. The faster it moves the shorter it gets in the direction of motion.
The object in this question moves and then stops moving. So it's length first contracts and then expands to its original length when the motion stops.
The speed doesn't have to be anywhere near the speed of light. When the object moves its length contracts no matter how fast or slow it's moving.
Fire Service Day
International Firefighters' Day (IFFD) is observed on May 4. It was instituted after a proposal was emailed out across the world on January 4, 1999 due to the deaths of five firefighters in tragic circumstances in a bushfire in Australia.
Answer:
23.0 s
Explanation:
Given:
v₀ = 0 m/s
v = 19.8 m/s
a = 4.80 m/s²
Find: Δx and t
v² = v₀² + 2aΔx
(19.8 m/s)² = (0 m/s)² + 2 (4.80 m/s²) Δx
Δx = 40.84 m
v = at + v₀
19.8 m/s = (4.80 m/s²) t + 0 m/s
t = 4.125 s
The elevator takes 40.84 m and 4.125 s to accelerate, and therefore also 40.84 m and 4.125 s to decelerate.
That leaves 291.3 m to travel at top speed. The time it takes is:
291.3 m / (19.8 m/s) = 14.71 s
The total time is 4.125 s + 14.71 s + 4.125 s = 23.0 s.