Mechanical engineer Interview Questions | Glassdoor

# Mechanical engineer Interview Questions

"When interviewing candidates for the role of mechanical engineer, employers look for candidates who are enthusiastic to create innovative designs, analyses, and methods of production for mechanical systems. Expect to answer engineering questions that will assess your knowledge of the field as well as your creative problem-solving abilities to turn a theoretical device into a real product. In addition, come ready to discuss examples of past projects or designs and how you would excel in a team-oriented setting."

## Top Interview Questions

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

Sep 7, 2015
 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 steelStrength 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.

### Senior Mechanical Engineer I at Northrop Grumman was asked...

Apr 26, 2014
 What has been your active role in the team process you're currently working with?2 AnswersExplained details of daily involvement, software used, level of completion of initial input received, and final deliverable.I quote the repairs and write up the job router steps to include R & R parts, inspection. Testing, and FAA 8130

### Mechanical Engineer at Stanley Black & Decker was asked...

Nov 16, 2013
 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 possible1 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

Apr 14, 2016

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

Oct 20, 2011
 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. 13 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 ResponsesConsidering 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 itselfThey 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.The two vehicles are identical, so both have the same power plants, and if they are rolling under power with the same control settings they will reach there at the same time.

Feb 22, 2013

Mar 9, 2012

### Mechanical Engineer at Intel Corporation was asked...

Dec 6, 2013
 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 rocksAnswer 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 ResponsesArchimedes 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 > waterDown. 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.

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

Jan 21, 2012
 You're in a row boat, which is in a large tank filled with water. You have an anchor on board, which you throw overboard. Does the water level in the tank rise or fall? 6 AnswersWater level in the tank will fall. because amount of water displaced by Anchor on board is larger than amount of water displaced by Anchor thrown overboard.Actually I feel the water level won't change. Since, the anchor is thrown from the boat there are two situations. a. Before being thrown : The anchor is in the boat and it's weight is accounted by the volume submerged. b. After being thrown: The anchor is now transferred from the boat to the tank. So even though the water level increases, the volume of the boat submerged, decreases. In essence one balances the other and there shouldn't be any change in the water level.Depends on the size and weight of the anchor.Show More ResponsesBy Archimedes Principle, water is displaced by Anchor's volume. Putting a new anchor down, and assuming that will not affect the boat's relative position with the water level, more water is displaced. The volume of water equals to the volume of anchor. You can even find the amount by mass of water being displaced by running volume x rho. This answer assumes no ripple effects. Assumes any the person's motion does not cause boat to move its height position at all.Not enough information to determine the answer. If the anchor is attached to the boat and does not rest on the bottom of the tank, the water would rise since the displacement caused by the boat wouldn't change, but you are adding the volume of the anchor..When an object is submerged in water , the lift/buoyant force on it is equal to the weight of water displaced. Case 1 Mw1*g = (Mb +Ma)*g ; Mw = dw*(A*h1) h1 = (Mb+Ma)/(dw) Case 2 , Boat is floating and anchor is completely submerged. h2 = (Mb)/(dw) +Ma/(d_steel) , where d_steel is density of steel > density of water (dw) clearly h2 < h1 , so the water level falls

Jul 14, 2009