Mechanics 1 Flashcards
explain how you would measure the acceleration in a laboratoey
- (draw diagram of trolley
- arrange suitable weights to hang over the edge of the table so that the trolley is moving with an acceleration
- run the paper tape through a ticker tape timer
u : s/(0.02 x dots)
v: s/(0.02 x dots)
a = (v-u)/t
state the principle of conservation of momentum
when two or more bodies interact in a closed system the total momentum of the bodies before the interaction equals the total momentum of the bodies after the interaction
which direction should the gas in an aircraft be expelled for it to be slowed down
the same direction as the motion
explain how the principle of conservation of momentum is applied to changing the direction un which a spacecraft is travelling
if a gas is expelled in a direction perpendicular to the motion of the spacecraft, the gas has a momentum in this direction and the spacecraft has an additional momentum in the opposite direction.
the extra momentum us added to the original momentum of the spacecraft and will cause the spacecraft to change direction
describe an experiment to find the resultant of 2 vectors
3 newton balances on a board (diagram), 1 and 2 are perpendicular and connected to board
pull balance 3 and then connect it to board
vector sum of forces 1 on 2 read on newton balances is force 3
force to push a wheelchair up a ramp is equal to what?
component of weight of the person acting down the ramp
Newton’s second law
when a resultant external force acts on a body the rate of change of momentum of the body is proportional to this force and takes place in the direction of the force
why does a sky diver reach a constant speed?
the skydiver falls down due to gravity, the air resistance will build up and eventually will equal the force of gravity, total resultant force is zero - no acceleration
describe an experiment to measure g due to free fall
draw diagram; (soft iron electromagnet, steel ball, trap door, millisecond timer)
values of distance measured from bottom of steel ball to trap door, electromagnet demagnetised, timer starts, trapdoor stops timer
graph when measuring g x axis
2 x distance
graph when measuring g y axis
time squared
give 2 precautions for accuracy when measuring g
avoid the error of parallax when measuring s
use large values of distance, smaller % error
define force
force i that which causes acceleration
define momentum
mass x velocity
establish the relationship force x mass = acceleration
force α rate of change of momentum F α (mv - mu)/t F α m((v-u)/t) F α ma F = kma, k=1, F=ma
minimise the effect of friction when measuring PCM
polishing the table
minimise the effect of gravity when measuring PCM
keep the table perfectly horizontal
Principle of concentration of momentum
energy cannot be created nor destroyed but it may be changed from one form to another
when a basketball loses kinetic energy where does it go
becomes sound or heat energy
what is friction
a force that opposes the relative motion of 2 bodies in contact
give 2 ways of minimising the effect of air resistance when measuring g
use a small dense ball
use a smooth ball
Newton’s first law
a body continues in a state of rest or uniform motion in a straight line unless a resultant external force acts on it
Newton’s third law
to every action there is an equal and opposite reaction
when investigating f minimise the effects of gravity when measuring f α a, why would the graph not go through the origin? 2
friction between the trolley and the table could be responsible for the graph not passing through the origin - polish the table to resolve the problem
the table might have been sloped, levelling the table would resolve this problem
3 ways to make a trolley move at a constant acceleration
adjust the slope of the table
lubricate the trolley wheels
make sure the table is polished to reduce friction
constant velocity on TTT
the dots on the tape are equally spaced
2 points of accuracy when verifying PCM
- avoid using trolleys of very small mass and avoid very small values of velocity, greater % error
- avoid error of parallax when measuring distance along the tape with meter stick
derive v² = u² + 2as
v = u + at v² = (u + at)² v² = u² + 2uat + at² v² = u² + 2a(ut +1/2 at² ) v² = u² + 2as
centripetal acceleration
v² /r
