# Mechanical Engineering Interview Questions

Mechanical engineering interview questions shared by candidates

## Top Interview Questions

You will likely be asked simple technical questions (e.g. solve an equation or diagnose an issue). As an example for a mechanical engineer, "how does an easy bake oven work?" The point is to answer the question as fully as possible 1 AnswerExplain about how the light bulb generates heat through the filament which provides both radiation and convection heating to bake the item. The oven provides insulation maintaining the heat. Write out the appropriate equation for bonus points |

### Mechanical Engineer at Tesla was asked...

Asked how the strength to weight ratio of aluminum and steel compared. 3 Answersstrength-to-weight ratio in typically the material's strength (which is force per unit area upon failure) divided by its density. Aluminum has a tensile strength of 572 MPa and a density of 2.81 g/cm^3 which computes to . Steel, on the other hand has a tensile strength of 505 MPa and a density of 8.00 g/cm^3. So, as can be seen, aluminum has a higher strength-to-weight ratio than steel Strength to weight ratio can be defined properly by the Yield strength (which defines the maximum stress that a material can handle before plastic deformation) to Density (mass/volume). Aluminum (6061) yield strength : density is 250MPa : 2080 kg/m^3 Stainless Steel cold rolled yield strength : density is 500MPa : 8000kg/m^3 For the same volume of material, the ratios are 1/8 for aluminum to 1/16 for stainless steel. You're getting twice as much the amount of strength on the aluminum per given volume than on the steel. Other two answers here are kinda wrong and honestly I think they're missing the point of the question. Strength is entirely dependent on alloy. Some aluminum alloys will have a higher strength/weight than some steel alloys, and vice versa. Unless the interview specifies specific alloys, you really can't make a blanket statement about "steel vs aluminum." You can, however, make general statements about stiffness. Almost all the densities and elastic moduli of aluminum or steel are nearly constant across the alloys, and actually for straight tension they have very similar stiffness/weight. The difference comes in bending. The same weight of aluminum has a much large cross section, and therefore a much larger moment of inertia, so an aluminum beam in buckling or bending will be stiffer than steel. Hope this helps. |

You are in a boat in a pool with a rock in your hand. You throw the rock into the pool. Does the water level rise, drop, or stay the same? 10 Answersdepends on how big the pool is and how accurately you can measure the water rise you're already in the pool with the rock, so the water displaced is the same...this other guy is stupid If the rock were neutrally buoyant the water level would remain the same. It is heavier than water which causes it to displace more than its own volume while in the boat compared to at the bottom of the lake. Therefore the water level of the lake would go down. Show More Responses At the moment the rock leaves your hand the water falls in the pool. When the rock enters the water the water level of the pool rises again to the level it had before you threw it. really? I thought the water would go up ? These answers are troubling. The only correct answer so far is Ben. The water level goes down. I'm not a mechanical engineer, but I did stay in a Holiday Inn Express last night. I hope no one else who has answered this question here (except for Homebrook) is a mechanical engineer. When you add the volume of the rock and subtract the volume of water previously displaced by the boat+rock, there is no change in the water level of the pool. Another way to answer is: The water level measured at the side of the pool remains the same. The boat becomes more buoyant and the water level measured at the side of boat falls. The weight of the boat plus you plus the rock has already displaced the height of the water. The only time the water level will change will be when the rock is mid air. M no Bbbbbbbbbbbbbbbbbbvvbvbbvbbb. B.B. BNb. Bbbb Bbvbbbbbbb Bbbbbbbbb B.B. Bbbbb V bbbb BNb B.B. BNb Bbbbbb BNb BNb Bbbb. BNb B b. Bbbbbbbb. N n. Bbbb. B B.B. N BNb bbb Nnnnn Nnnn nnn Nnnn Nn N. Nn N M Mm. I. N. M M m Mmm n nnn Mmm mmnmmmnm Mmnmmmmm Mmm my Mmmm Mmm Mmm Mmmmmmmmm m Mmmmmmmm It will raise by the same volume of the rock. |

What has been your active role in the team process you're currently working with? 1 AnswerExplained details of daily involvement, software used, level of completion of initial input received, and final deliverable. |

### Mechanical Engineer at Tesla was asked...

If two vehicles are identical, except for one weighing twice as much as the other vehicle, and they roll down a hill, which car reaches the bottom first? Neglect air resistance. Assume the extra mass is in the body of the vehicle. 12 AnswersThey get there at the same time. The heavier car reaches the bottom first because the rotating inertia (wheels) of that car makes up a smaller percentage of of its mass. This is why the question mention /where/ the extra mass of the heavier car is. Heavier vehicle reaches first. Because the wheel of heavier vehicle have a bigger angular acceleration due to heavier body weight. Show More Responses Considering the wheels to be a small part of the vehicle mass, and neglecting external force, here air resistance, Law of conservation of energy is applicable. Mgh = ½ Mv^2 + ½ Iω^2 assuming ½Iω^2 to be a very small quantity considering mass of the vehicle, we can neglect the same. Thus, velocity square is directly proportional to twice the product of g*h, as mass cancels out in the above equation. Thus, velocity is seen to be independent of the mass of the vehicle, and thus both of them will reach at the same velocity. from an energy standpt PE = KE + Work PE= KE(tran) + KE(rot) + work m(overall)gh= 1/2m(overall)v^2+#wheels*(1/2(m(wheel)*radius^2)*angularvelocity^2)+ m(overall)*g*h*cos(angle of slope)*dist so if we take out all mass overall... and some algebra v^2 = 2[ gh - #wheel*(1/2*(mwheel/moverall)*radius^2*angularvelocity^2)- ghcos(theta)*d] terminal velocity is dependent on mwheel/moverall, if car is heavy on body, theoretically it should be faster than a lighter car. The vehicles are no longer identical. how long is the hill? if short - light car will reach first. if long enough, then heavy car (which has lower acceleration, but can attain higher terminal velocity) -- heavy car must overcome greater inertial delay at top of hill, so gets a slower start. Light weigh car reach first, because the heavier body vehicle will stop the rotation by its mass itself They reach at the same time. Assuming the mass is included in the body and minimal friction and no air resistance, mass will not be a factor. PE will be completely transformed to KE by the bottom of hill meaning mgh=.5mv^2, mass cancels out meaning mass doesn't matter. This is similar to dropping a feather and a bowling ball on the moon. No air resistance so they hit the ground at same time. Don't over think it. That's the worst thing you can do in an interview. Same time... Don't listen to the rest of the shmos what we are really worried about here are the cars acceleration From FDB: F = ma = mgcos(theta) - FrictionForce = mgcos(theta) - mu*NormalForce = mgcos(theta) - mu*mgsin(theta) Divide both sides by m, and there is no mass left in equation... just a = gcos(theta) - mu*gsin(theta) Therefore, the equation is independent of mass and they arrive at the same time. They should reach to the bottom at the same time. The solution is as follows: Based on "Law of conservation of energy", assuming the mass of both vehicles are M1 = m, M2 = 2m, where, the velocity for both vehicles are v_1 and v_2, and angular velocity for both vehicles are omega_1 and omega_2, the inertia for both vehicles are J1 and J2. The height of hill is h The equations are listed as: M1*g*h = 1/2 * M1 * (v_1^2) + 1/2 * J1 * (omega_1^2) (1) M2*g*h = 1/2 * M2 * (v_2^2) + 1/2 * J2 * (omega_2^2) (2) Note that rolling is in the plane of X-Z about Y-axis, based on "Parallel Axis Theorem", Jyy = 1/12 * M * R^2, where R is defined as the half width of the vehicle. Thus, J1 = 1/12 * M1 * R^2; J2 = 1/12 * M2 * R^2, due to both vehicle are identical in shape. Also, v_1 = R*omega_1; v_2 = R*omega_2; substituting M1, M2, J1, J2, v_1, v_2, into (1) and (2), such that: omega_1 = omega_2 = sqrt(2*g*h/(R+1/12)) (unit: rad/sec). Therefore, v_1 = v_2 = R*sqrt(2*g*h/(R+1/12)) (unit: m/sec); Assuming the length of slope from the top to the bottom is "L", the time ("T") for both vehicle rolling to the bottom is: T = L/v_1 = L/v_2 = L/(R*sqrt(2*g*h/(R+1/12))) (unit: sec). In conclusion, these two vehicles will spend identical time on rolling to the bottom. Angle of the hill? Has the car the same bearing size in the wheels? Much mass is more radial load and then more friction. The question needs to be more specific. |

### Mechanical Engineer Intern at Nokia was asked...

If you have a refrigerator in an isolated room (no heat in or out) and left the door to the refrigerator open, what would happen to the temperature to the room? Would it go up, down or say the same? 12 AnswersIf the door to the refrigerator is left open, the frige has to work harder because now it has to try to cool the entire room rather than just the inside of the frige. The coils and condenser in the back of the frige would create more heat thus heating the room up. The temperature of the room would stay the same - the key is the fact that it is in an isolated room. There is no heat exchange between the room and it's external surroundings. The refrigerator will warm up the room. If you look on the back of the refrigerator, you will see metal grating. Touch it. Its warm! A refrigerator is transporting heat from the inside cavity to the outside. However, the power cord running from the wall is pumping energy into the refrigerator/room. Energy is powering the refrigerator. It is also running an irreversible process, the energy dissipates out as heat and work (mostly heat), making the net temperature of the room increase. Show More Responses I propose the room remains constant - but for the following reason. The room is reported to be isolated. I denote that to be a cube with no walls, windows, doors, plumbing, OR conduit or an electrical box that would allow cable or air to move within or without the isolated cube. Logically, in that the fridge is not powered, it is not generating heat through the use of the motor, condenser or heat - exchange coils. Really, it doesn't matter what the answer is... you've just got to defend it logically. If the fridge were powered - but was an excessively large model (as you might find in a grocery store walk in) the room might cool. If it were a smaller unit - the motor would have to work overtime to try and keep it cool - thus heating the room. Just be creative! That's what they're looking for. Can you think on your feet. Aa The room's temperature will be exactly as the refrigerator's temperature. Heat will be absorbed by the grating metal on the back of the refrigerator, so no need to worry about where the heat that refrigerator produces go. Majority of the answers here are wrong. A refrigerator is a heat pump that move thermal energy opposite to the direction of spontaneous heat flow by absorbing heat from a cold space and releasing it to a warmer one. There is some work required to move this thermal energy from Cold to Hot. If we assume that the amount of work used to move this energy is negligible, if you leave a refrigerator door open in an isolated room, the room temperature will stay the same. https://en.wikipedia.org/wiki/Heat_pump https://en.wikipedia.org/wiki/Refrigerator If its an isolated room the frig will not be able to be plugged in to an outlet. So remains the same The room temperature will remain the same. The reason for this lies in its basic principle of vapor compression cycle. Its true that refrigerator transfers the heat from one place to another. But one has to remember that the door is open. So, As heat is extracted by refrigerant and thrown in room using condenser and since the room is isolated and refrigerator door is open.. the same heat will be added inside refrigerator and same refrigeration cycle continues after that. In a way refrigerator is not able to cool anything. it is just continuously maintaining energy equivalence. In this case, there is a net gain of energy from the refrigerator outlet into the room and no loss of energy out of the room. Thus, the room will warm up since there is a gain of energy. Part of the room's temperature would decrease slightly. The other part of the room's temperature will stay the same. Since the refrigerator's energy is not large enough to cool the whole room it will cool a small portion of the room. the temperature inside the room will increase |

in a boat on a lake with a rock, throw the rock in the water which way does the water level move? here is a memory card- what is it made out of and how was it made? 8 Answersdown (if density of rock > water), true for most rocks Answer 0 = down ?? No. Up. The rock displaces water in the lake to move up. Actually the water initially has a circular pattern of vertical waves since water in mostly incompressible ... Show More Responses Archimedes Principal. Weight of rock is displacing water upwards when in the boat. When in the water it is displacing its volume. Water has to go down since the density of most rocks > water Down. If rock is solid, which means the volume of the boat below the water level cannot be fully filled by the rock. the water level goes down. Think about an extreme case. You have an small item made of the worlds most dense material in the hull of the boat. Even though the volume of the item is small the weight is very heavy. This pulls the boat down and since the volume that the boat displaces will be much higher then that of the small item, when the item is thrown over board, the boat lifts further out of the water displacing less water causing the level to decrease. no change in water level. it will be the same as it was when the rock was on the boat. Water level goes down, since boat gets lighter on removing any size of rock in turn making the boat go up and water level go down than initial measured level. |

If you were in a dark closet with 49 white socks and 1 black one.how many socks would you pick so as to ensure that you exit the closet with a pair of similar colored socks 12 Answers3 socks this is probability qtn and always prober provide prober answer 3 3 socks Show More Responses All of them. In a dark closet it is hard to distinguish colors. 3 At least 3 two I would make 25 pairs of socks in the dark then choose 2 of the complete pairs. It’s a high possibility I would come out with a white pair! 3 3 1 I would pick as many as I needed to make sure that they matched. |

You are in a boat and you threw the anchor into the river. The anchor settled on the lake floor. What happens to the level of water before and after the anchor is dropped ? 5 AnswersDrops. Nothing happened to the water level because its a flowing river, not a standing body of water. Well which is it a river or a lake? Depends on the mass of and volume of the anchor. Is the mass enough to use the boat to displace more water than the volume of water displaced by the anchor being moved into the water? Show More Responses In general the level of the water drop because the density of the steel (for example) or other material of the anchor is bigger than the density of the water. I'm not in a lake I am on a river. |

### Mechanical Engineer at Cummins was asked...

All questions were behavioral and nothing specifically difficult. 2 AnswersDid they get back to you with a second interview? How did you come to know that you didn't get offer,any email,call ?and when did your application got updated? |

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