Work
What is the formula for work?
W = Fd
Provide a formula for power that is NOT P= (W/t)
A 1,500 kg car has 270,000 J of KE. What is its speed?
v = 18.97 m/s
Water with a mass of 2 kg is heated from 20°C to 70°C. Using a specific heat of 4,186 J/kg°C, this is the amount of heat energy absorbed, in joules.
Q=418,600 J
When is work negative?
When the force and displacement are in opposing directions
Rob and Peter move a sofa 3 m across the floor by applying a combined force of 200 N horizontally. It takes them 6 seconds. What is their power?
P = 100 W
(100 Watts)
A bird with 882 J of GPE has a mass of 0.5 kg. How high is it flying?
h = 180 meters
A heater outputs 6,000 J of useful energy from 8,000 J of input energy. This is its efficiency, as a percentage.
75%
When is W=0?
When the force and displacement are perpendicular to each other?
A 70-kg cyclist develops 210 watts of power while pedaling at a constant velocity of 7 m/s east. What average force is exerted eastward on the bicycle?
F = 30 N
A 2 kg ball is dropped from a height of 5 meters. What is its speed just before it hits the ground?
v ≈ 9.9 m/s
A 3 kg mystery metal absorbs 54,000 J of heat and its temperature rises from 25°C to 175°C. What is the specific heat capacity of the metal?
c = 120 J/kg°C
How much work is done lifting an 8 kg box 2 m off the floor?
W ≈ 156.8 J
If a Dodge Hellcat produces 535,000 W of power. How much horsepower does it have? (Reminder: 1 hp = 746 W)
535,000W=717HP
A spring with k = 400 N/m is compressed 0.05 m. Calculate its Elastic PE ( PEs)
PEs = 0.5 J
A coal power plant burns fuel releasing 500,000 J of input energy. It loses 175,000 J to exhaust gases and 80,000 J to friction. This is the plant's efficiency as a percentage.
49%
Barry & Sidney pull a 30 kg wagon with 500 N over 20 m. Force at 30° to horizontal. Calculate the work done.
W = 8660 J
*Daily Double*A 60 kg sprinter accelerates up a flight of stairs, rising 4 meters vertically in 3 seconds. What is her power output, in watts, rounded to the nearest whole number?
P=784 W
How does doubling the speed of a moving object affect its kinetic energy?
Doubling the speed quadruples the kinetic energy
A 4 kg iron bar (specific heat 450 J/kg°C) starts at 20°C and absorbs 72,000 J of heat. This is the final temperature of the iron bar, in °C
Tf = 60°C