When a lead bullet hits a large solid target at high speed, its entire kinetic energy is converted into heat. for simplicity, assume that all that heat is concentrated in the bullet rather than the target. if the bullet’s initial temperature is 29°c, how fast would it have to move before the collision in order to have 29 % of its mass melted after the collision? lead has a melting temperature 327.3 °c, a specific heat of 128 j/kg · k and latent heat of fusion 24500 j/kg. answer in units of m/s.

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Clothing made of several thin layers of fabric with trapped air in between, often called ski clothing, is commonly used in cold climates because it is light, fashionable, and a very effective thermal insulator. so it is no surprise that such clothing has largely replaced thickand heavy old-fashioned coats. (a) consider a jacket made of five layers of 0.1-mm-thick synthetic fabric (k = 0.13 w/m·°c) with 1.5-mm-thick air space (k = 0.026 w/m·°c) between the layers. assuming the inner surface temperature of the jacket to be 28°c and the surface area to be 1.25 m2, determine the rate of heat loss through the jacket when the temperature of the outdoors is 0°c and the heat transfer coefficient at the outer surface is 25 w/m2·°c. (b) what would your response be if the jacket is made of a single layer of 0.5-mm-thick synthetic fabric? what should be the thickness of a wool fabric (k = 0.035 w/m·°c) if the person is to achieve the same level of thermal comfort wearing a thick wool coat instead of a five-layer ski jacket?

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