Engineering Mechanics(Mechanical Engineering ) Questions and answers for exam Preparation

Question 1. The resultant of the two forces ‘P’ and ‘Q’ is ‘R’. If ‘Q’ is doubled, the new resultant is perpendicular to ‘P’. Then

P = Q
Q = R
Q = 2R
None of these

Explanation:-

Answer: Option B. -> Q = R

Question 2. The point, through which the whole weight of the body acts, irrespective of its position, is known as

Moment of inertia
Center of gravity
Center of percussion
Center of mass

Explanation:-

Answer: Option B. -> Center of gravity

Question 3. The centre of gravity of an isosceles triangle with base (p) and sides (q) from its base is

$$\frac{{\sqrt {4{{\text{p}}^2} - {{\text{q}}^2}} }}{6}$$
$$\frac{{4{{\text{p}}^2} - {{\text{q}}^2}}}{6}$$
$$\frac{{{{\text{p}}^2} - {{\text{q}}^2}}}{4}$$
$$\frac{{{{\text{p}}^2} + {{\text{q}}^2}}}{4}$$

Explanation:-

Answer: Option A. -> $$\frac{{\sqrt {4{{\text{p}}^2} - {{\text{q}}^2}} }}{6}$$

Question 4. A pair of smith's tongs is an example of the lever of

Zeroth order
First order
Second order
Third order

Explanation:-

Answer: Option B. -> First order
First Order Levers: First class levers have the fulcrum between the force and the load. In using a screwdriver to lift the lid from a paint tin you are moving the effort over a greater distance than the load.
Second Order Levers: In second class levers the load is between the effort (force) and the fulcrum. A common example is a wheelbarrow where the effort moves a large distance to lift a heavy load, with the axle and wheel as the fulcrum.
Third-order levers: With third class levers the effort is between the load and the fulcrum, for example in barbecue tongs.
Source : primaryconnections.org.au

Question 5. The moment of the force ‘P’ about ‘O’ as shown in the below figure is

P × OA
P × OB
P × OC
P × AC

Explanation:-

Answer: Option C. -> P × OC

Question 6. The resultant of two equal forces P making an angle $$\theta ,$$ is given by

$$2{\text{P}}\sin \frac{\theta }{2}$$
$$2{\text{P}}\cos \frac{\theta }{2}$$
$$2{\text{P}}\tan \frac{\theta }{2}$$
$$2{\text{P}}\cot \frac{\theta }{2}$$

Explanation:-

Answer: Option B. -> $$2{\text{P}}\cos \frac{\theta }{2}$$

Question 7. The linear acceleration (a) of a body rotating along a circular path of radius (r) with an angular acceleration of $$\alpha $$ rad/s2, is

$${\text{a}} = \frac{\alpha }{{\text{r}}}$$
$${\text{a}} = \alpha {\text{r}}$$
$${\text{a}} = \frac{{\text{r}}}{\alpha }$$
None of these

Explanation:-

Answer: Option B. -> $${\text{a}} = \alpha {\text{r}}$$

Question 8. If a number of forces are acting at a point, their resultant is given by

$${\left( {\sum {\text{V}} } \right)^2} + {\left( {\sum {\text{H}} } \right)^2}$$
$$\sqrt {{{\left( {\sum {\text{V}} } \right)}^2} + {{\left( {\sum {\text{H}} } \right)}^2}} $$
$${\left( {\sum {\text{V}} } \right)^2} + {\left( {\sum {\text{H}} } \right)^2} + 2\left( {\sum {\text{V}} } \right)\left( {\sum {\text{H}} } \right)$$
$$\sqrt {{{\left( {\sum {\text{V}} } \right)}^2} + {{\left( {\sum {\text{H}} } \right)}^2} + 2\left( {\sum {\text{V}} } \right)\left( {\sum {\text{H}} } \right)} $$

Explanation:-

Answer: Option B. -> $$\sqrt {{{\left( {\sum {\text{V}} } \right)}^2} + {{\left( {\sum {\text{H}} } \right)}^2}} $$

Question 9. A framed structure is perfect, if the number of members are __________ (2j - 3), where j is the number of joints.

Equal to
Less than
Greater than
None of these

Explanation:-

Answer: Option A. -> Equal to

Question 10. Moment of inertia of a circular section about an axis perpendicular to the section is

$$\frac{{\pi {{\text{d}}^3}}}{{16}}$$
$$\frac{{\pi {{\text{d}}^3}}}{{32}}$$
$$\frac{{\pi {{\text{d}}^4}}}{{32}}$$
$$\frac{{\pi {{\text{d}}^4}}}{{64}}$$

Explanation:-

Answer: Option C. -> $$\frac{{\pi {{\text{d}}^4}}}{{32}}$$