Bill is running late to his final exam and decides to drive 60 mph in a 50 zone

Question

Bill is running late to his final exam and decides to drive 60 mph in a 50 zone (drive 1.2 times faster than the speed limit) in order to arrive at the exam on time. He tells his passenger, Maria, that the shouldn't worry about this, because the car will only have 1.2 times as much kinetic energy at 60 mph as it would at 50 mph. Do you agree with Bill? How many times more kinetic energy will the car actually have? Carefully explain your answer in terms of ratio reasoning, and draw a box around your final answer! A complete essay is not required for this problem. A uniform disk spins counterclockwise like a wheel on a frictionless axle with initial angular speed 10.0 rad/s. At t = 0 s, a brake pad is applied to the face of the wheel at a distance 15.0 cm from the axle and begins applying a frictional force of constant magnitude 3.00 N. The wheel's rotation comes to a stop at t = 8.00 s. Calculate the moment of inertia of the wheel. Show all work and units, and draw a box around your final answer!

Explanation / Answer

No we donot agree with Bill.let m= mass of car

KE1 = 1/2 m (50)^2

KE 2 = 1/2 m (60)^2

we divide the two kinetic energies , 1/2 m will cancel

so KE2/KE1 = (60)^2 / (50)^2

KE2/KE1 = 36/25 = 1.44

so KE2 = 1.44 KE1

so kinetic energy at 60 mph is 1.44 times kinetic energy at 50 mph   

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