What net external force is requiered?

AI Thread Summary
To determine the net external force required to accelerate a 1500kg car from rest to 100km/h in 10 seconds, the correct approach involves using the formula F=ma. The acceleration must be calculated in meters per second squared, which requires converting 100km/h to meters per second, resulting in approximately 27.78 m/s. This gives an acceleration of 2.778 m/s² when divided by 10 seconds. Multiplying this acceleration by the mass of the car yields a force of approximately 4167N, aligning with the book's answer. Proper unit conversions and calculations are essential for accurate results.
metalx1000
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My wife is taking a Physics class and is having some trouble. I've never taken physics but I've tried to help, with no luck.

Homework Statement


What net external force is required to accelerate a 1500kg car from rest to 100km/h in 10 seconds?

Homework Equations


She believes that the right equation is:

F=ma

The Attempt at a Solution



100km/1hour x 1hour/60sec = 100/60 = 1.7km/s

a=(1.7 km/s)/10s
a=0.17s/km

F=1500kg x 0.17s
F=255
-------------------------------
So we got '255N'The book says the answer is '4167N'
But it does not say how to get this.

She is studying for a test tomorrow.
Any help would be great.

Thanks
 
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metalx1000 said:
My wife is taking a Physics class and is having some trouble. I've never taken physics but I've tried to help, with no luck.

Homework Statement


What net external force is required to accelerate a 1500kg car from rest to 100km/h in 10 seconds?

Homework Equations


She believes that the right equation is:

F=ma

The Attempt at a Solution



100km/1hour x 1hour/60sec = 100/60 = 1.7km/s

a=(1.7 km/s)/10s
a=0.17s/km

F=1500kg x 0.17s
F=255
-------------------------------
So we got '255N'


The book says the answer is '4167N'
But it does not say how to get this.

She is studying for a test tomorrow.
Any help would be great.

Thank
You just changed the clock. There are 3600 seconds in an hour! Also, watch your units...your acceleration should be in meters/sec^2, not km/sec^2, to get the proper unit of the external force in Newtons.
 
Thank you

after posting we did convert it to metters but did not catch the min and seconds mixup.

Thanks again
 
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