Test 1 Mechanics Flashcards
(22 cards)
Potential energy formula?
PE=mgΔh
Kinetic energy formula?
KE=1/2mv^2
What is power?
power=energy transfer / time. U: Watt (joule/s) also the rate of doing work. p=work done/time => P=Fv
What is a resistive force?
Forces that act on a moving body in the opposite direction of movement. main resistive f is friction (drag + air resistance).
Resistive forces formula?
W = ΔEp + ΔEk (e.g. if there is a resistive force of 0.3 N then that is substituted into W)
A crane lifts a load of 1500kg a height of 25m at a steady rate, in a time of 2 min. Power of crane?
A man of mass 70kg runs up 2 flights of stairs in 30 seconds. What is his useful power output?
What is a Sankey Diagram?
A diagram that shows the major energy transfers including energy losses through a closed system. Input according to scale comes in on the left and waste goes as an arrow downwards, the width of the arrow indicating size of energy. The useful energy goes on straight ahead, also width of arrow indicating energy size.
What is momentum?
Change of momentum?
P = mv
The rate of change of momentum of an object is proportional to the resultant force acting on the objcect.
Change of momentum is according to NL2 F = mΔv / Δt
What is an impulse?
Impulse = F Δt
NSL can be rearranged: FΔt = Δ(mv)
Change in momentum
To reduce the impact force the time during which the collision takes place should be increased.
Integral of force-time graph.
What types of energy is there?
Chemical
Kinetic
Thermal
Sound
Electrical
Light
Newton’s first law?
An object will remain at rest, or continue to move with uniform velocity, unless acted upon by an external force. Net forces + inertia
Newton’s second law?
The rate of change of an object’s linear momentum is directly proportional to the resultant external force. The change in momentum takes place in the direction of the force. The acceleration of an object increases when the force is increased but decreases when the mass is increased: F=ma
Newton’s third law?
When body A exerts a force on body B, body B exerts an equal but opposite force on body A. Forces are created in pairs.
What is energy?
The ability to do work.
Work done = energy transferred
Efficiency?
Efficiency=useful output power of the device / input power to the device
Elastic collision?
Kinetic energy is conserved, no energy is transferred to the surroundings. Only perfectly elastic is at molecular level w/ brownian motion. To some degree newton’s cradle.
Inelastic collision?
Kinetic energy is not conserved, energy is transferred to the surroundings.
Car crashes or pretty much any collision.
Collision EQ?
m1u1 + m2u2 = m1v1 + m2v2
where m = mass
u= initial velocity, v = final velocity
Explosions?
Momentum before is zero since system is not moving. Momentum after will still equal zero since there is a recoil. Therefore,
m1v1=m2v2.
Force equations?
F=ma according to NL2
Also, F=Δ(mv)/Δt according to same
Difference between scalar and vector quantity?
Scalar has magnitude only. A vector has magnitude and direction.
