Usain Bolt (and in fact most world-class sprinters, both male and female), can r

Question

Usain Bolt (and in fact most world-class sprinters, both male and female), can run the 100m sprint in roughly 10 seconds. Your friend on the UCLA track team claims that she can achieve a top speed of 40 mph when she runs the 100m sprint. Is she likely telling the truth? Explain your reasoning. An advertising for Toyota's prototype electric family sedan that the car can sustain a straight-line acceleration equal to half the acceleration due to gravity for about 20 seconds. Does this sound reasonable? Explain your reasoning. As a bank robber sitting in the vault planning how you can maximize your wealth, do you fill your suitcase with $100 bills or with gold bars? Your suitcase is the only method of transporting the loot out of the bank.

Explanation / Answer

2.1

Speed of Usain Bolt = vbolt = d/t = 100m/10s = 10m/s

Speed of friend = vfriend = 40mph = 40mile/hour = (40*1609)/(3600s) = 17.88m/s

vfriend > vbolt

Which is not acceptable

2.2

acar = g/2 = (9.8m/s^2)/2 = 4.9m/s^2

vf=vi+at = 0 + 4.9*20 = 90m/s = 324km/h

Which is not acceptable because this speed is much higher for sedan cars. Hence not reasonable.

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