- #1

Cole07

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## Homework Statement

A 600- kg ice boat moves on runners on essentially frictionless ice. A steady wind blows, applying a constant force to the sail. At the end of an 7- s run, the acceleration is 0.4 m/s2. What was the acceleration at the beginning of the run? Answer: 0.4m/s

What was the force due to the wind?

Answer:240N

What retarding force must be applied at the end of 4 s to bring the ice boat to rest by the end of the next 4 s? (The wind is still blowing. Assume the boat was at rest at time t = 0.)

Answer:?

**2. Governing equations**

Vf=Vi+at

## The Attempt at a Solution

I understand the first two questions i have them figured out but the last one i can't seem to figure out. i used the equation

0.4=0+a(4)

and i get a=0.1 which i multiply by 600kg using the formula EF=ma and get EF=60N i don't understand why this is wrong any help would be appreciated.