Suppose a 36 kg squid (not including water) at rest at the surface of the water brings in and quickly ejects 3.0 kg of water to achieve a takeoff speed of 3.5 m/s these are typical numbers.Īt what speed does the squid eject the water? Some squid do this at the surface of the ocean, thus launching themselves into the air-a particularly effective escape strategy. In terms of this model, how many rotations does she complete in the 1.3 s that she holds the pike position? 14kg⋅m^2ģ.3 rotations We've seen that squid can escape from predators by ejecting water. In terms of this model, what is her angular speed in the pike position? In terms of this model, what is her moment of inertia in the pike position? In terms of this model, what is her initial moment of inertia? Next, assume that when she goes into a pike position, she really does fold her body exactly in half. First, model her 50 kg, 1.8 m body as uniform. We can use a simple model to understand what happens next. She then tucks into a pike position, with her body essentially folded in half. Her body is in a relatively slow rotation, with an angular speed of 4.0 rad/s. What is the angular momentum of the bar about the axle? 2.6 kg⋅m^2/s A diver leaves the platform with her body straight. What is the direction of the third piece? 15.55 m/sĤ5 degrees north of east The 630 gg bar is rotating as shown in The third piece has twice the mass as the other two. Two pieces of equal mass fly off south and west, perpendicular to each other, at 22 m/s. What is their speed just after he grabs her? 2.4 m/s A firecracker in a coconut blows the coconut into three pieces. Just as Erica reaches the high point of her bounce, Danny is moving upward past her at 4.4 m/s. With what speed should you impact the Cadillac to bring it to a halt? 2 mph Erica (39 kg ) and Danny (46 kg ) are bouncing on a trampoline. Seeing the situation, you realize you have just enough time to drive your 2000 kg Volkswagen head-on into the Cadillac and save the children. What is the average force on the pigeon during the impact? 30 m/sĤ80 N The parking brake on a 1000 kg Cadillac has failed, and it is rolling slowly, at 4 mph, toward a group of small children. What is the final speed of the falcon and pigeon? The collision between the birds lasts 0.015 s. The falcon strikes the pigeon and grabs it in her talons. The falcon reaches a vertical speed of 45 m/s before striking the pigeon, which we can assume is stationary.
The falcon slows to a near stop, then goes into a dive-called a stoop-and picks up speed as she falls. A 480 g peregrine falcon high in the sky spies a 240 g pigeon some distance below. Sometimes they strike at high enough speeds that the force of the impact disables prey birds. If the bullet leaves the muzzle at a speed of 500 m/s, what is the final speed of the man? 7.1×10^−2 m/s Peregrine falcons frequently grab prey birds from the air. The mass of the man together with the rifle is 70 kg, and the mass of the bullet is 10 g. Suppose a man standing on frictionless ice fires a rifle horizontally. How big a push will it give? Let's find out by doing a calculation in a very artificial situation. 2.4 X10^4 Nģ.1×10^5 N In principle, when you fire a rifle, the recoil should push you backward. What is the maximum a bone can be compressed in Dyn/cm^2? Which of the following is the reason that we would recommend that the man bend his legs while landing from such a fall?Īs part of a safety investigation, two 1800 kg cars traveling at 24 m/s are crashed into different barriers.įind the average force exerted on the car that hits a line of water barrels and takes 1.8 s to stop.įind the average force exerted on the car that hits a concrete barrier and takes 0.14 s to stop. What would be the average force he experiences in this scenario? Dyne is also a unit of force and 1 Dyn = 10^−5N. For these calculations, g = 10 m/s^2 With how much force can the "leg" be compressed before breaking? What is his speed just before he hits the ground? If he lands "stiff legged" and his shoes only compress 1 cmcm, what is the magnitude of the average force he experiences as he slows to a rest? If he bends his legs as he lands, he can increase the distance over which he slows down to 50 cmcm. Assume his acceleration once he hits the ground is constant. A man with a mass of 70 kg falls from a height of 6 m.
Human bone can be compressed with approximately 1.7 × 1088 N/m^2 before breaking.
While unrealistic, we will examine the forces on a leg when one falls from a height by approximating the leg as a uniform cylinder of bone with a diameter of 2.3 cm and ignoring any shear forces.
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