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23 Cards in this Set
- Front
- Back
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When a forces makes an object move over a distance what is is being done on an object?
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Work is done
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How is the amount of work done is related to energy transferred?
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Work done equals the amount of energy transferred.
IE work done increase either the gravitational potential energy, kinetic energy, or the elastic potential energy of the object by the exact same amount. |
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Rearrange the equation
work done = force × distance moved or W = F × d to solve for force and distance |
Force= work / distance
Distance = work / force |
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Rearrange the equation
gravitational potential energy = mass × g × height GPE = m × g × h to solve for mass, g, and height |
h= GPE/ m / g
g = GPE / m/ h m = GPE / g / h |
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What are the units for each of the variables in the following equation?
W = F × d |
work, W is measured in joules (J)
force, F is measured in newtons (N) distance, d is measured in metres (m) |
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Calculate the distance moved by a force of 8N when it does 72J of work.
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W = F x d
becomes: d = W ÷ F = 72 J ÷ 8 N distance moved = 9 m |
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What are the units for each of the variables in the following equation?
GPE = m × g × h |
GPE is measured in joules (J)
mass, m is measured in kilograms (kg) gravitational field strength, g is measured in newtons per kilogram (N/kg) height, h is measured in metres (m) |
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Calculate the gravitational potential energy gained by a student of mass 70kg climbing a flight of stairs of height 4m.
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GPE = m x g x h
= 70kg x 10N/kg x 4m GPE = 2 800 J |
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If an object is moving what type of energy does the object have?
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Kinetic energy
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What is the formula for kinetic energy and what are the units for each of the variables?
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kinetic energy = ½ x mass x (speed)2
KE = ½ x m x v2 kinetic energy, KE is measured in joules (J) mass, m is measured in kilograms (kg) speed, v is measured in metres per second (m/s) |
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Calculate the kinetic energy of a child of mass 60kg moving at 3 m/s.
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KE = ½ x m x v2
= ½ x 60kg x (3m/s)2 = ½ x 60 x 9 = 30 x 9 kinetic energy = 270 J |
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Calculate the speed of a car of mass 1200kg if its kinetic energy is 15 000J.
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KE = ½ x m x v2
15 000J = ½ x 1200kg x (speed)2 15 000 = 600 x (speed)2 15 000 ÷ 600 = (speed)2 25 = (speed)2 speed = square root (25) speed = 5 m/s |
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If there is no loss to due to drag how does the amount of GPE a falling ball has at the beginning have compared to the kinetic energy right before it hits the ground?
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If there is no significant air resistance then conservation of energy results in gravitational potential energy being converted into kinetic energy as an object falls.
gain in KE = loss of GPE |
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What is the formula for power that relates the amount of energy and time? What are the units for each variable
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power = work done / time taken
P = W/t power, P is measured in watts (W) work done, W is measured in joules (J) time, t is measured in seconds (s) |
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Calculate the power of a motor that exerts a force of 40N over a distance of 2m for 10seconds.
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W = F d
= 40 N x 2 m work done = 80 J P = W / t = 80J / 10 s power = 8.0 W |
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What is the formula for momentum?
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momentum = mass x velocity
OR p = m x v |
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In the momentum equation what are the units for each quantitiy?
momentum = mass x velocity |
mass is measured in kilograms (kg)
velocity is measured in metres per second (m/s) momentum is measured in: kilogram metres per second (kg m/s) |
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Because momentum is a vector what matters beside the amount of momentum?
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The direction of the momentum
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Calculate the mass of a car that when moving at 25m/s has a momentum of 20 000 kg m/s.
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p = m x v
becomes: m = p ÷ v = 20000 kg m/s ÷ 25 m/s mass = 800 kg |
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What must occur for there to be a change in the velocity of an object?
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A force will cause the velocity of an object to change and therefore also its momentum.
The greater the force the faster the momentum changes. |
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In the force impulse equation
F = (mv – mu) / t What are each of the variables and their units |
mass is measured in kilograms (kg)
velocity is measured in metres per second (m/s) Force is measured in Newtons (N) v is the final speed (m/s) u is the inital speed (m/s) |
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Calculate the time taken for a force of 6000N to cause the momentum of truck to change by 42000 kgm/s.
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force = momentum change ÷ time taken
becomes: time taken = momentum change ÷ force = 42000 kgm/s ÷ 6000 N force = 7 seconds |
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What does the following statement mean
Momentum is conserved in any collision or explosion provided no external forces act on the colliding or exploding bodies. |
With no outside forces the
momentum before = momentum after For the collision |
