Question: A 250-V, 4-pole, wave-wound d.c. series motor has 782 conductors on itsarmature. It has armature and series field resistance of 0.75 ohm. The motor takesa current of 40 A. Estimate its speed and gross torque developed if it has a flux per pole of 25 mWb Answer: Step 1 Mechanical Engineering homework question answer, step 1, image 1 Mechanical Engineering homework question answer, step 1, image 2 Step 2 Mechanical Engineering homework question answer, step 2, image 1 Step 3 Mechanical Engineering homework question answer, step 3, image 1

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Question:

Suppose two children are using a uniform seesaw that is 3.00 m long and pivoted at 2 m from the left edge, and a 30.0 kg child sits 1.40 m to the right  of the the center of mass of the seesaw. Seesaw weighs 5 kg.

a. Calculate where the second 18.0 kg child must sit to balance the seesaw. [ 5 points]

b. How far will the child be from the center of mass of the seesaw? [ 2 points]

c. How far will the child be from the left edge of the seesaw? [3 points] 

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Answer:

(a)

Length of seesaw l = 3 m

Pivot point is at 2m from left

Centre of mass of seesaw is at 1.5 m, therefore, distance of centre of mass from pivot point is

lc = 2 - 1.5 m =0.5m

The child sits 1.40 m to the right of the the center of mass of the seesaw. So, distance of child from pivot point is

lR = 1.40 - 0.5 m = 0.9 m, towards right

mass of child at right mR = 30kg

mass of seesaw,mc= 5 kg

mass of child at left, mL = 18 kg

distance of left child from pivot point = lL

Child on the left and centre of mass of seesaw provide a anticlockwise torque whereas student on the right provide a clockwise torque.

For rotational symmetry

                                                          (Ans)

The child should sit at 1.36 m from the pivot point, towards left

 

(b)

The center of mass of the seesaw is at 0.5m from the pivot

Distance of child to the centre of mass is

                   (Ans)

 

(c)

The distance of left edge to the pivot point is 2m

Distance of child from the left edge is

                   (Ans)