Question

A small sports car and a pickup truck start coasting down a 12 m hill together,...

A small sports car and a pickup truck start coasting down a 12 m hill together, side by side. The mass of the sports car is 640 kg and the mass of the pickup truck is 1280 kg (twice the mass of the sports car). Assuming no friction or air resistance, what is the kinetic energy of each vehicle at the bottom of the hill? Give your answers in joules. HINT: How does the kinetic energy of a vehicle at the bottom of the hill compare to the potential energy of the vehicle at the top of the hill? Use your answer to this hint to guide your strategy. (a) What is the kinetic energy of the sports car? J (b) What is the kinetic energy of the pickup truck? J What is the speed of each vehicle at the bottom of the hill? Give your answers in m/s. (c) What is the speed of the sports car? m/s (d) What is the speed of the pickup truck? m/s

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Answer #1

(a)

apply conservation of energy

kinectic energy of sports car = potetntial energy of sports car

= (640) (9.8) (12)

=75264 J

kinectic energy of pickup truck = potetntial energy of pickup truck

= (1280) (9.8) (12)

=150528 J

speed of sprots car is

kinectic energy of sports car = 1/2 mv^2

v= sqrt 2(kinectic energy of sports car)/m

= sqrt 2 ( 75264 J)/640

=15.33 m/s

kinectic energy of pickup truck = 1/2 Mv^2

v= sqrt 2(kinectic energy of pickup truck)/M

= sqrt 2 ( 150528 J)/1280

=15.33 m/s

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