Mechanics Flashcards
a vector quantity has both…
Direction and magnitude (oh yeah)
If I drive 15 km to Pak’n’save (detouring to recoil at New World prices), and Pak’n’save is 10 km away from where I started, which of these quantities is distance and which is displacement?
The distance is 15 km, and the displacement is 10 km.
At the top of the path of a projectile, vertical velocity is…
0 m/s
How would you add two vectors that are neither parallel or perpendicular to each other (i.e. are weird)
Resolve both into x and y components, then add.
What is Newton’s third law?
Every action has an equal and opposite reaction.
What is Newton’s first law?
The law of inertia (the movement of an object will not change unless acted upon
What is Hooke’s law?
F = k x
F= force on spring
k= spring constant
x= extension/compression from equilibrium
Every spring has an elastic limit. What happens to a spring past it’s elastic limit?
The spring deforms, and Hooke’s law no longer holds (f and x no longer increase proportionally)
What is torque?
Force applied at a distance
If an object is not moving / at an equilibrium, what two quantities are balanced?
Clockwise torque = Anticlockwise torque
Up force = down force
When working with an object that is fixed at two sides (say, a bridge), choose where as a pivot point?
a pier as a pivot point (it is arbitrary, but easy to work with)
What is frequency?
Oscillations per second ( n/t )
What is period?
Seconds per oscillation ( t/n )
How do you calculate circular speed?
v= d/t, since d= circumference, d= 2(pi)r, velocity is v = 2(pi)r/t
How do you calculate centripetal acceleration (the acceleration curving the path of the object closer to the centre)?
a=v squared/r
How do you calculate centripetal force?
As f=m x a, centripetal force is f = (m x v squared) / r
In the “Jelly spinning on the plate” example, why does the jelly stay on the plate?
The friction between the jelly and the plate provides centripetal force that negates the effect of inertia.
What is momentum?
Mass in motion
What is impulse?
Change in momentum
If I dropped a coin from my roof, and I threw a coin straight upwards, what would be the downwards acceleration for both objects?
They would both be 9.8 m/s squared.
If you do not consider friction, energy is…
conserved (not destroyed, only converted to a different form.
What is the equation for momentum?
p=mv
What is the equation for impulse?
▲p= ft
There are two rotisserie chickens. One is dropped on a pillow, and another is dropped on a concrete slab. How can the equation for impulse help explain the state of the chickens after the drop?
When the chickens slow down, they must lose their momentum (p=mv, v is 0), so they each must experience an impulse (▲p). Impulse is force exerted over time (▲p=ft), and it is force that causes the chicken to turn into a Jackson Pollock painting. The pillow can deform, so it allows for more time for the chicken to decellerate (larger t means less f), and the chicken is relatively intact. The concrete cannot deform, so it has a very small t number, so it must have a large force to exert the proper impulse, splatting the chicken.
Because energy is conserved (and friction is not considered in exam papers), what equations can be seen as equivalent?
1/2 m v squared = m g h (or 1/2 k x squared if you’re a spring)
▲Ek = ▲Ep
If you kick a ball on a curve-like path, not considering friction, what values can be considered constant?
Vertical acceleration and horizontal speed
What is the difference between an elastic and an inelastic collision?
Kinetic energy does not change in an elastic collision, energy is converted into different forms in an inelastic collision.
What is conserved in both elastic and inelastic collisions?
Momentum (only if you consider the collision a whole system)
