11. Momentum & Impulse

A 95-kg fullback is running at 3.0 m/s to the east and is stopped in 0.75 s by a head-on tackle by a tackler running due west. Calculate the impulse exerted on the tackler.

(II) A 95-kg fullback is running at 3.0 m/s to the east and is stopped in 0.75 s by a head-on tackle by a tackler running due west. Calculate the average force exerted on the tackler.

(III) Air in a 120-km/h wind strikes head-on the face of a building 45 m wide by 75 m high and is brought to rest. If air has a mass of 1.3 kg per cubic meter, determine the average force of the wind on the building.

(II) A 95-kg fullback is running at 3.0 m/s to the east and is stopped in 0.75 s by a head-on tackle by a tackler running due west. Calculate the impulse exerted on the fullback.

(III) (a) Calculate the impulse experienced when a 68-kg person lands on firm ground after jumping from a height of 2.8 m.

(b) Estimate the average force exerted on the person’s feet by the ground if the landing

(c) with bent legs. With stiff legs, assume the body moves 1.0 cm during impact, and when the legs are bent, about 50 cm. [Hint: The average net force on him, which is related to impulse, is the vector sum of gravity and the force exerted by the ground. See Fig. 9–42.] We will see in Chapter 12 that the force in (b) exceeds the ultimate strength of bone (Table 12–2).

A rocket with a total mass of 330,000 kg when fully loaded burns all 280,000 kg of fuel in 250 s. The engines generate 4.1 MN of thrust. What is this rocket's speed at the instant all the fuel has been burned if it is launched in deep space? If it is launched vertically from the earth?