- #1
physicsgal
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"a person drives their 1452 kg car along a straight road at a constant velocity of 30 m/s east. their brakes suddenly give out. they put the car in neutral and let is coast for 25 seconds. the air drag decelerates the car to a velocity of 25 m/s east. (assume a frictionless surface)."
b) assume the average acceleration while the car is decelerating
so it's just (25 m/s - 30 m/s)/25 s = -0.2 m/s^2?
c) determine the average force of air against the car
f = ma
= (1452 kg)(-0.2)
= 290.4 N
d) after coasting for 25s. they pull their car handbrake to slow the car to a stop. this take 3 seconds. what is the force applied by the handbrake? assume that the force exerted by the air remains constant and is equal to the forced determined in part (c).
so i assume i find acceleration by (0 - 25)/time
but for the time is it (25s-3s) or (3s - 25s)?
and then i just the acceleration times the mass of car = handbrake force?
any help will be appreciated!
~Amy
b) assume the average acceleration while the car is decelerating
so it's just (25 m/s - 30 m/s)/25 s = -0.2 m/s^2?
c) determine the average force of air against the car
f = ma
= (1452 kg)(-0.2)
= 290.4 N
d) after coasting for 25s. they pull their car handbrake to slow the car to a stop. this take 3 seconds. what is the force applied by the handbrake? assume that the force exerted by the air remains constant and is equal to the forced determined in part (c).
so i assume i find acceleration by (0 - 25)/time
but for the time is it (25s-3s) or (3s - 25s)?
and then i just the acceleration times the mass of car = handbrake force?
any help will be appreciated!
~Amy