Initial velocity (u) = 90km/hr = 90/3.6 m/s = 25m/s
final velocity (v) = 18km/hr = 18/3.6 m/s = 5m/s
acceleration = (v-u)/t = (5-25)/4 = -5 m/s2
change in momentum = m(v-u) = 1200(5-25) = -24000 kg•m/s
F = ma = 1200 x -5 = -6000 N
Answer:
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Explanation:
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D. 128.25 because force=mass x acceleration
There's not enough information given in the problem to calculate that answer.
A leaf falling from a tree on Earth, a sheet of printer paper falling off the back
of a truck on Venus, and a steel ball sinking through a bucket of Scotch whiskey
on Mars, might all reach the bottom in 0.75 second. The time it would take each
of them to fall the same distance through a vacuum in the same place would be
different, and the 0.75 second is not enough to enable you derive it ... <em>even</em> if
you <em>did</em> know the acceleration of gravity in each place. All you can say is that
without resistance, it would fall faster, and hit bottom in <em>less than</em> 0.75 second.