Long-Answer Exam Qs Flashcards
1
Q
Explain why a raindrop falling vertically through still air reaches a constant velocity.
A
- initially raindrop accelerates due to weight/gravity
- resistive forces also acts on raindrop but is initially lower than force of gravity
- these forces increase with speed
- eventually resistive force equals weight
- resultant force is now zero as the forces are balanced
2
Q
Explain why driver would be less injured in a collision if the air bag inflates than he would be if unrestrained.
A
- moving driver has momentum (
- in sudden impact, momentum must be lost in a short time
- F = Δ(mv) / Δt
- air bag increases stopping contact time
hence reduces force
3
Q
Why is the driver of a car fitted only with seat belts more likely to be injured than if an air bag was fitted?
A
→ seat belt applies force to smaller area than air bag
→ causing greater pressure on parts of body
4
Q
Explain what happens to the air as an air bag inflates with ref. to pressure, volume & temperature.
A
- initially air occupies small volume at high pressure
- on expansion volume increases & pressure decreases
- temperature of gas decreases as it expands
5
Q
What is the pressure in an air bag caused by?
A
caused by change in momentum in molecular collisions
6
Q
What is KE equal to when the gain in KE is more than the loss of GPE?
A
KE = loss in GPE + work done - wasted energy
