You have been called to testify as an expert witness in a trial involving a head-on collision. Car A weighs 1515 1515 lb and was traveling eastward. Car B weighs 1125 1125 lb and was traveling westward at 44.0 44.0 mph. The cars locked bumpers and slid eastward with their wheels locked for 20.5 20.5 ft before stopping. You have measured the coefficient of kinetic friction between the tires and the pavement to be 0.750 0.750 . How fast (in miles per hour) was car A traveling just before the collision

Speed = 72.76mph

Explanation:

east direction signifies +

Therefore,

1515E -1125(45) = -2640

F = -2640×0.75 = -1980lbs

so,

-1980lbs = Ma

but m = 2640×g where g = 32.2 ft/s²

so,

a = -(1980/2640g) = -0.75×g = -24.15ft/s² = dv/dt

0 = V-24.15t

V =24.15t

22.5 = Vt -12.07t²

22.5 = 24.15t² - 12.07t² = 12.07t²

t = 1.37 seconds

Therefore,

V = 24.15 × 1.37 seconds = 33.1 ft/s

converting to mph gives

33.1 ft/s = 22.6 mph

now back to momentum

1515 E -1125(45) = 2640 V

1515 E = 50625+59664

Speed = 72.76 mph

72.8mph

Explanation:

east is positive

1515 E -1125(45) = 2640 V

F = 2640*.75 = -1980 pounds

so

-1980 pounds = m a

but m = 2640/g where g = 32.2 ft/s^2

so

a = -(1980/2640)g = -.75 g = -24.15 ft/s^2

= dv/dt

0 = V-24.15 t so V =24.15 t

22.5 = V t -12.07 t^2

22.5 = 24.15 t^2 - 12.07 t^2 = 12.07 t^2

t = 1.37 seconds

so

V = 24.15 * 1.37 seconds = 33.1 ft/s

convert that to mph

33.1 ft/s = 22.6 mph

now back to momentum

1515 E -1125(45) = 2640 V

1515 E = 50625+59664

E = 72.8 mph

-first use of geothermal energy occurred more than 10,000 years ago in north america by american paleo-indians

-the first industrial use of geothermal energy began near pisa, italy in late 18th century

-in 1904, italian scientist piero ginori conti invented the first geothermal electric power plant in which steam was used to generate the power

-with the above experiment, the first geothermal plant in usa started in 1922 with a capacity of 250 kilowatts

-however, in 1946 first ground-source geothermal heat pump installed at commonwealth building in portland, oregon

-during the 1960’s, pacific gas and electric began operation of first large scale geothermal power plant in san francisco, producing 11 megawatts

-in 1973, when oil crisis began many countries began looking for renewable energy sources and by 1980’s geothermal heat pumps (ghp) started gaining popularity in order to reduce heating and cooling costs

-as effect of climate change started showing results, governments of various countries joined hands to fight against it, for which kyoto protocol was signed in japan in 1997, laid out emission targets for rich countries and required that they transfer funds and technology to developing countries, 184 countries have ratified it

hope this