1. You are driving home from school steadily at 90 km/h for 160 km . It then beg

Question

1. You are driving home from school steadily at 90 km/h for 160 km . It then begins to rain and you slow to 61 km/h instantly. You arrive home after driving 5.0 hours.

A. How far is your hometown from school?

Express your answer using two significant figures.

B. What was your average speed?

2. A car traveling 98 km/h is 220 m behind a truck traveling 87 km/h.

How long will it take the car to reach the truck?

Express your answer using two significant figures.

3. A sports car accelerates from rest to 85 km/h in 4.2 s . What is its average acceleration in m/s2.

Express your answer using two significant figures.

4. A car slows down from 30 m/s to rest in a distance of 78 m.

What was its acceleration, assumed constant?

Express your answer using two significant figures.

5. A light plane must reach a speed of 39 m/s for takeoff.

How long a runway is needed if the (constant) acceleration is 2.9 m/s2 ?

Express your answer using two significant figures.

6. In coming to a stop, a car leaves skid marks 82 m long on the highway.

Assuming a deceleration of 3.50 m/s2 , estimate the speed of the car just before braking.

Express your answer using two significant figures.

Explanation / Answer

1)Given,

v = 90 km/h ; d = 160 km ; v' = 61 km ; t = 5 hr

A)We know that

v = d/t => t = d/v

t1 = 160/90 = 1.78 h

t2 = 5 - 1.78 = 3.22 hr

D = d1 + d2

D = 160 + 61 x 3.22 = 356.42 km

Hence, D = 356.42 km

B)Vav = total dist/time

Vav = 356.42/5 = 71.28 km/h

Hence, Vav = 71.28 km/h

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