Question

A cartoon shows two friends watching an unoccupied car in free fall after it has rolled off a cliff. one friend says to the other "It goes from zero to sixty miles per hour in about three seconds." is this statement correct?

Answer 1

The acceleration of gravity is 32.2 ft/sec^2.
After 3 seconds of free fall, the car is falling at 96.6 ft/sec.

60 mph is 88 ft/sec.

Let's look at it in two ways:

==> 96.6 is 9.8% greater than 88 .

==> It takes the car (88/32.2)=2.73 seconds to reach 60 mph. 3 is 9.8% greater than 2.73 .

Either way you look at it, the rough number is within 10% of the real number. That's plenty close enough to say that they're "about" the same.

It really depends on what the friends mean when they say "about". As an engineer, my personal feeling is that anything less than 10% off is a beautiful match.

Answer 2

1 mile = 1609 meters.60 miles = 96 540 meters.1 hour = 3 600 seconds.
Then:The velocity V = 96 540 / 3600 ≈ 26.8 m/s
Acceleration of free falla = V/t = 26.8/3 ≈ 8.9 m/c².
But it should be (excluding air resistance of 9.8 m/s².
Answer: the statement is wrong!