# When eagles hunt for fish, they catch their prey by diving into the water from a great height….

When eagles hunt for fish, they catch their prey by diving into the water from a great height. They learned to use gravity to accelerate, and to control their speed using the drag force of their wings. Let’s consider an eagle that starts its dive with a speed of 5 km/hr horizontally, and from a height of 140 m above the ground. The eagle dives with a constant downwards acceleration reaching a vertical speed of 80 km/hr at a distance of 20 m above the ground. For this example, neglect horizontal acceleration during the dive.

a) Calculate the magnitude of the vertical acceleration during the eagle dive.

b) Draw a force diagram showing all the forces acting on the eagle during its dive. Describe the different forces and motions at stake as well as the relative magnitudes of the forces.

c) Let’s consider the eagle mass to be 8.0 kg. Calculate the vertical drag force provided by the wings (assumed the drag constant during the dive).

Problem 1.3 Let’s consider a manual coffee grinder as shown in Figure 1. This manual grinder comes with a handle of length d=20cm. The grinder starts turning when the torque t applied to the grinder is more than 0.5 N.m.

a) Determine the direction and magnitude of the minimal force to apply on the handle to start the grinder.

b) What will happen if a force of 5N is applied in the Y axis direction while the handle turns (the magnitude and direction of the force stay the same during motion)? Describe the motions taking place.

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