Jean camps beside a wide river and wonders how wide it is. She spots a large rock on the bank directly across from her. She then walks upstream until she judges that the angle between her and the rock, which she can still see clearly, is now at an angle of = 45° downstream (Fig. 1-12). Jean measures her stride to be about one yard long. The distance back to her camp is n = 150 strides. About how far across, both in yards and in meters, is the river?

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1 yd

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2 m

Figure 1-12.

A 90 m long train begins uniform acceleration from rest. The front of the train has a speed of 20 m/s when it passes a railway worker who is standing 174 m from where the front of the train started. What will be the speed of the last car as it passes the worker? (See Fig. 2-36.)

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1 m/s

Figure 2-36.

Figure 3-42.

(a) A skier is accelerating down a 30.0° hill at 2.90 m/s² (Fig. 3-42). What is the vertical component of her acceleration?

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1 m/s² down.
(b) How long will it take her to reach the bottom of the hill, assuming she starts from rest and accelerates uniformly, if the elevation change is 355 m?

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2 s

One 2.7 kg paint bucket is hanging by a massless cord from another 2.7 kg paint bucket, also hanging by a massless cord, as shown in Fig. 4-39.

Figure 4-39.

(a) If the buckets are at rest, what is the tension in each cord?

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1 N (lower bucket)

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2 N (upper bucket)
(b) If the two buckets are pulled upward with an acceleration of 1.70 m/s² by the upper cord, calculate the tension in each cord.

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3 N (lower bucket)

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4 N (upper bucket)

At what minimum speed must a roller coaster be traveling when upside down at the top of a circle (Fig. 5-33) if the passengers are not to fall out? Assume a radius of curvature of 8.2 m.

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1 m/s

Figure 5-33.