What net external force is requiered?

[metalx1000]

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

 

[PhanthomJay]

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.

 

[metalx1000]

Thank you

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

Thanks again