1. Why is the cooling unit placed at the top of the refrigerator?a)Cold air falls and warm air is displaced upwards.b)Cold air is a bad conductor so heat is not conducted into the fridge.c) Cold air is a good conductor so heat is conducted out of the fridge.d) cold air stops at the top and so prevents convection.2. Which substance is a liquid room temperature of 25*C?a) Melting point -218 boiling point -193b) Melting point -39 boiling point 357c) melting point 44 boiling point 280d) melting point 119 boiling point 444 3) a long bar copper is heated evenly along its length, what happens to the bar?a) it becomes lighterb) it becomes longerc) it becomes shorter d) it bends at the end.4) four blocks, made of different materials, are each given the same quantity if internal (heat) energy. Which block has the greater thermal capacity?a) Temperature rise 2*Cb) Temperature rise 4*Cc) Temperature rise 6*Cd) Temperature rise 8*C
Ceramic are much better, you do not get the noise cheap semi metallic pads make.Less brake dust, more stopping power and overall last longer.Depending on your vehicle, the dealership i went to, did not offer ceramic pads to purchase, just their oem semi metallic, so of course that's what they are going to recommend.I did a brake job for some friends and bough the pads at a store they wanted it from and they were a low quality semi metallic pad, it would squeal loudly at slow stopping speeds that drove them nuts.Within a week later they had me get ceramic pads to throw on and love them.
ceramic brake pads semimetallic brake pads
are they better? No. as far as stopping it makes no difference. The difference is ceramic pads do not give off near as much brake dust and they tend not to squeak as much. But other than that they are really not better like i said as far as stopping.
1. a is the answer. Cold air is heavier and so falls, thus displacing warm air upwards and setting up a convection current inside without a fan. 2. b is the right answer. See its melting point has to be less than 25 and its boiling point has to be more than 25 for it to remain liquid at 25 C. Only the substance at b with a melting poin t of -39 C and a boiling point of 357 meets that condition. 3. b is the right answer. Whether it is heated uniformly or at one end, it gets heated and with heat comes elongation for most materials. It may bend at one end if some constraints are imposed and the heating is non-uniform and that is why the question confirms that the bar is heated evenly along its length. 4. a is the answer. The block with maximum thermal capacity will have the minimum temperature rise. One assumption in this question is that the mass of the blocks and the initial temperature are equal. Remember the formula Q m.s.(t2 - t1) where Q is the quantity of heat supplied, m is the mass, s the specific heat and t1, t2 are the initial and final temperatures respectively. Here Q, m and t1 are kept constant and only s changes for each material, so t2 changes inversely with s. Knowing the right answer becomes fun when we know why our answers are right. Good luck.
