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physics exam 2
| Question | Answer |
|---|---|
| A 1000-kg car and a 2000-kg car are hoisted to the same height. Raising the more massive car requires -less work -as much work -twice as much work -four times as much work -more than four times as much work | twice as much work |
| An object has gravitational potential energy due to its -speed -acceleration -momentum -location -none of the above | location |
| A machine puts out 100 watts of power for every 1000 watts put into it. The efficiency of the machine is | 10% |
| A clerk can lift cylindrical packages 1 meter vertically, or can roll them up a 2-meter-long ramp to the same elevation. With the ramp, the applied force required is about -half as much -the same -twice as much -four times as much | half as much |
| A motorcycle moving at 50km/h skids 10 m with locked brakes. How far will it skid with locked brakes when traveling at 150 km/h? -10m -30m -50m -90m | 90m d2 = 10m (150km/h / 50km/h ) ^2 = 10m(3)^2 = 10m x 9 = 90m |
| A cannonball has more kinetic energy than the recoiling cannon from which it is fired - is more concentrated - meets less resistance than the cannon on the ground - acts over a longer distance | acts over a longer distance |
| A car's engine is 20% efficient. When cruising, the car encounters an average retarding force of 1000 N. If the energy content of fuel is 40 megajoules per liter, how many kilometers per liter does the car achieve? -8 -10 -12 -14 -none of the above | 8 Useful energy = Fuel Energy Content x Efficiency Useful energy = (40 x 10^6 J/L) x 0.20= 8 x 10^6 J/L W = F x d 8 x 10^6J = 1000N x d -> D = 8x10^6 J / 1000 N = 8000m d in km = 8000m x 1km/1000m= 8km |
| Two identical arrows, one with twice the speed of the other, are fired into a bale of hay. Compared with penetration of the slow arrow, the faster arrow penetrates - the same distance - two times as far - four times as far - more than four times | Four times as far This is because it is kinetic energy is proportional to the square of the velocity. Doubling speed quadruples kinetic energy |
| About 40J is required to push a crate 4 m across a floor. If the push is in the same direction as the motion of the crate, the force on the crate is about - 4N - 10N - 40N -160 N | 10N W = Fs 40 J = F 4m 40 J / 4m = f 10 J/M = 10 N |
| If you do work on a skateboard loaded with friends in one-third the usual time, you expend - one third as much power - the usual power - three times the usual power - need more information | three times the usual power P = Wlt Pnew = W / t new = W / 1/3 t old = 3 x W / t old = 3 P old |
| A miracle car with a 100% efficiency engine burns fuel having a 40-megajoules-per-liter energy content. If air drag and overall frictional forces at highway speeds totals 1000N, what distance per liter can be achieved on the highway? - 30 km - 40 km | 40 km E = 40 x 10^6 J (one liter of fuel) W = F x d -> E = F x d -> d = E/F d = 40x10^J / 1000N d = 40000 m x 1km/1000m d = 40 km |
| The unit kilowatt-hour is a unit of - energy - momentum - power - time | energy |
| A bicycle that travels four times as fast as another when braking to a stop will skid -twice as far -four times as far - eight times as far -sixteen times as far | sixteen times as far. kinetic energy is proportional to square of velocity. Increasing speed by four increases kinetic energy by 4^2 which is 16 |
| At what point in its motion is the KE of a pendulum bob at a maximum? | The KE is at a maximum at the bottom of the swing since all PE has turned into KE |
| At what point is PE at a maximum? | PE is at a maximum when the bob is at the max height |
| How do the amounts of PE and KE compare when the bob swings by the point that marks half its maximum height? | When the bob is at half its max height, the PE is also at half its max, along with KE. PE and KE are |
| Danny Diver has a mass of 50 kg and steps off a diving board 10 m above water. a) What is D's initial potential energy? b) The instant before D hits the water, what is his kinetic energy? c) Determine D's speed the moment right before he hit the water? | a) PE = mgh = 50 kg x 10 m/s^2 x 10m = 5000J b) KE_{bottom} = PE_{top} = 5000J c) KE = (1/2) mv^2 V = (2 KE /m)^1/2) = 2 x 5000J / 50 kg) ^1/2 = 14.14 m/s |
| You can swing your legs to and fro more frequently when your legs are | bent |
| a coin and ring roll down an icnline at the same time. which is the first to reach the bottom | coin |
| for a system in mechanical equilibrium, the resultant | force and torque must be zero |
| The chef at the infamous Fattening Tower of Pizza tosses a spinning disk of uncooked pizza dough into the air. The disk becomes wider during its flight, while its rotational speed | slows because the angular momentum remains constant, the inertia increases due to change in mass distribution from center of rotation. angular velocity decreases to balance this out. |
| Centripetal force does no work on a circularly-moving object because | centripetal force has no component in the direction of motion |
| A torque acting on an object tends to produce | rotation because torque is the rotational equivalent of a force which produces an angular acceleration that leads to change in objects rotation, |
| The net force exerted on a car traveling in a circular path at a constant speed is | directed towards the center of the curve because the cars velocity is constantly changing direction which means its accelerating and towards the center of the path. |
| An industrial flywheel has a greater rotational inertia when most of its mass is | nearer the rim because the mass is farther from the center which magnifies the rotational inertia. |
| Describe how mass and the distribution of that mass affect rotational inertia | Distribution of mass affects the rotational inertia because the greater the inertia the farther mass from the axis but the less the inertia the closer to the mass to the axis. Mass affects the rotational inertia because less weight requires less force. |
| To tighten a bolt, you push with a force of 50N at the end of a wrench handle that is 0.35 m from the axis of the bolt. a) What torque are you exerting? | 17.5 N x m Torque = Force x Distance = 50 N x 0.35 m = 17.5 N x m |
| To tighten a bolt, you push with a force of 50N at the end of a wrench handle that is 0.35 m from the axis of the bolt. b) If you move your hand inward to be only 0.20 m from the bolt, to achieve the same torque, what force must you exert? | 87.5 N Torque = Force x Distance (new) Fnew = t / rnew = 17.5 N x m / 0.20 m = 87.5 N |
| To tighten a bolt, you push with a force of 50N at the end of a wrench handle that is 0.35 m from the axis of the bolt. c) do your answers depend on the direction of your push relative to the direction of the wrench handle. | Yes because torque depends of the angle of the force and wrench handle. |
| If a fictional shrinking man shrinks proportionately to 1/10 his original height, his weight will be multiplied by | 0.001 because weight is proportional to volume so it would be (1/10th)^3 which is 1/1000. |
| Compared to the volume of a kilogram of feathers, the volume of a kilogram of lead is | less because lead has a higher density than feathers so a kg of lead takes up less space than feathers. |
| Consider the fictional case of the incredible shrinking woman. If a fictional shrinking woman shrinks to 0.1 her original height, her total skin area shrinks to | 0.01 times its original value. because 0.1 x 0.1 = 0.01 because of being two dimensional measurement. |
| A spring is stretched 10 cm by a suspended 1-kg block. If two such springs side-by-side are used to suspend the 1-kg block, each spring will then stretch | 5cm since it is split between the 2 springs. |
| An iron block in a furnace is heated and consequently expands, which means that its density is | less because heating the block results in higher volume w/ constant mass meaning density decreases. |
| A metal block has a density of 5000 kg per cubic meter and a mass of 15,000 kg. What is its volume? | 3m^3 Density = m/V 5000kg/m^3 = 15000kg / v 5000kg/m^3 x v = 15000kg/ v x v v x 5000kg/m^3 = 15000kg v = 15000kg / 5000kg/m^3 v = 3m^3 |
| Compared to a bar of pure gold, the density of a pure gold ring is | the same because density does not change according to shape and size |
| Which is the greater amount for medication measured by mass? 1 gram or 1000 milligrams | they are the same |
| Compared with a solid steel bar having a rectangular cross-section, an I-beam has the advantage of | being lighter and stronger per bodyweight |
| A horizontal wooden beam sags a bit when supported at its end. In between the top and bottom surfaces is a region of -tension -compression -neither of these | neither of these |
| If the volume of an object were doubled while its mass remained the same, its density would | be half because density is mass divided by volume |
| If a pencil's length and diameter are both multiplied by 10, then its volume is multiplied by | 1000 (10x10) |
Created by:
edw13