mechanics (only non maths topics) Flashcards
newtons 1st law of motion
the velocity of an object will not change unless a resultant force acts on it
newtons 2nd law motion
Force ∝ rate of change of momentum
F = Δ(mv)/Δt
or (F=ma) (dont put this one as the asnwer tho)
newstons 3rd law of motion
if object A exertes a force on object B, then pbject B exerts a equal but opposite force on object A
the pair of forces in newtons 3rd law are always the ______ ______
give an example and one commenly thought of example that is not actually newtons 3rd law
same type
A) pushing against water
b) a book on a table is not an example of newtons 3rd law a the 2 forces acting upon teh book are not the same
momentum equation and units
momentum = mass x velocity
ρ = m x v (kgms^-1)
is momentum a scaler or a vector quantity
vector
assuming no external forces act, momentum is _______
conserved
what is a elastic collision
a collision where momentum and Ek is conserved (therefore NO enegy is dissipated as heat , sound ect)
what is a inelastic colision
a collision where Ek is not conserved (e.g therefore enegy IS dissipated as heat , sound ect)
tho momentum is conserved
in both elastic and inelastic what is always conserved
momentum
what is impulse
change of momentum
rearage the newtons second law equaiton to find impulse and give the units
F = Δ(mv)/Δt
Ft = Δ(mv) (just assuming Δt is t as you would in any suvat equation)
Ft = mv - mu where v is final valocity and mu is initioal velocity)
units = Ns
what is impulse defined as in terms of force and time
F x t
what is the area under a force x time graph
impulse
work done equation and units
wd=f x d jules(J)
(the force needs to be fixed) (can be constent or a avarge)
defonition of a jule
one jule is the work done when a force of 1 newton moves an object through a distance of 1 meter
what is the area under a force displacment diagram
word done
gice the 2 equations of power for mechanics and the unit
give 1 more power equation
power = wd/t therefore power = workdone per second
power = F x V
units = w
power=E/t
1 watt is ___ _____ __ _____
1 juel per second
exam questions (1m):
there are 2 sample wires but the second one has 3 x Lenth and 1/2 the diamitor what is the youngs modules of the new meterial in terms of E (youngs modules of the origenal meterial)
E
the youngs modules is a propity of a meterial thus not effected by the changing of dimensions
what word often siginifiers within a question that you are ment to use momentem equation within the question
collision
(and if they dont state weather the collision is inelastic or elastic)
what do 2 forces need to be to be newtons 3rd law pair foces (3)
- the forces need to have the same magnatude
- the forces need to be of the same type
- the forces need to act on 2 diffrent objects NOT the name on
GPE equation
mgh
interactions A:
a pellet hits a block and is imbeded,
interaction B:
a pellet hits a block and bounces back
in wich interaction does the block have the greatest v after the interaction
interaction B
because
ρ is a vector.
since the pellet and the block hgas the same momentum before the interaction but after the interaction the pellet has negetive vlocity.
as ρ is conserved.
after the interaction teh block must have greater ρ.
since the blocks mass stays the same.
the the v i fthe block must be greater to compensate for the negetive velocity of the pellet.
ρ after = ρ before
m1u1+m2u2=m1v1+m2v2
m1u1+m2u2 does not change
m1v1 decreases
so
m2v2 must increase
