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- Homework Statement
- This is actually from a Calculus textbook.

A car is traveling at 100 km/hr when the driver sees an accident 80 m ahead and slams on the breaks. What constant deceleration is needed to stop the car in time to avoid a multi-car pileup.

Book says the answer is 62,500 km/hr^2.

I teach Calculus (not for very long) and the book wants students to do this from an antiderivative perspective. I did not get the answer the book states. I used my prior Physics knowledge and used the "timeless" equation for distance to check my answer and did not get that answer the the book says. I just need someone to double check my work to see if it is safe to say the book is incorrect.

- Relevant Equations
- vf^2 = vi^2 + 2ax

v

v

x = 80,000 km

v

0 = 100^2 + 2a(80,000)

160,000a = -10000

a = -0.0625 km/hr^2

This is off by 1,000,000 times from the textbook answer. Am I missing something with units or something or is the book wrong?

_{f}=0 km/hrv

_{i}= 100 km/hrx = 80,000 km

v

_{f}^{2}= v_{i}^{2}+2ax0 = 100^2 + 2a(80,000)

160,000a = -10000

a = -0.0625 km/hr^2

This is off by 1,000,000 times from the textbook answer. Am I missing something with units or something or is the book wrong?

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