Engineering Mechanics – Assignment 1

1. What will change if the straight link BD is replaced by the curved link as

shown in the lecture?

a. Nothing

b. FBD of ABC

c. FBD of BD

d. FBDs of BD and ABC

Ans: a

2. When the extra weight W1 is added at point B, choose the option that best

describes the FBDs of links BD and ABC.

Ans: b

3. The pole AB shown in the picture is totally 15m long and has a uniformly

distributed mass of 150 kg. It is supported at both its ends on “smooth”

walls. What is magnitude of the reaction force at A? Take the value of the

gravitational acceleration to be 10m/s^2 (mark the option that is closest to

your answer)

a. 250 N

b. 300 N

c. 333 N

d. 376 N

Ans: c

4. Consider the previous question and assume now that the walls “aren’t

smooth”, would the reaction forces at A and B change? Would the value of T

(the tension in the cable) change? (Hint: no need of any calculation)

a. No, No

b. No, Yes

c. Yes, No

d. Yes, Yes

Ans: d

5. The extraction of a nail is greatly facilitated by a block placed under the head

of a claw hammer. Consider a 200 N pull on the handle, which is required to

pull the nail. Calculate the tension in the nail and enter a numeric answer in

Newton (the answer must match exactly).

Ans: 800 N

6. Consider the previous question. What is the magnitude of the force between

the head of the hammer and the block? (mark an answer closest to the answer

you obtain)

a. 343 N

b. 564 N

c. 850 N

d. 755 N

Ans: d

7. A person performs slow arm curls with a 90 N weight as shown in the figure.

The brachialis muscle group has a major role in this exercise. Determine the

magnitude of the force exerted by these muscles. (Consider the weight of the

forearm to be 14 N that is acting effectively at the point G)

a. 693 N

b. 750 N

c. 843 N

d. 945 N

Ans: a

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