Weighing with A 400 N Scale and 80 N Spring Dynamometer

In summary, a former student of mechanics has a scale with a capacity of 400 N and a small spring dynamometer with a capacity of 80 N. By exerting a pull of 76 N on the rope attached to the dynamometer, the student reads a normal reaction of 268 N on the scale. Using the equilibrium condition, the student can find T1 and T2, and ultimately calculate their mass. The range of weight that can be measured by this system is 76 N to 304 N.
  • #1
PFuser1232
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Homework Statement



A former student of mechanics wishes to weigh himself but has access only to a scale A with capacity limited to 400 N and a small 80 N spring dynamometer B. With the rig shown he discovers that when he exerts a pull on the rope so that B registers 76 N, the scale A reads 268 N. What is his mass ##m##? Also, what range of weight could be measured by this system?

Homework Equations



Since the student is in equilibrium:

$$\sum F_y = 0$$

The Attempt at a Solution



The normal reaction acting on the student is 268 N. There are two tensions acting on the student; ##T_1## and ##T_2## (see diagram).
##T_1## is clearly 76 N. However, I can't seem to find ##T_2##. How do I assign a value to ##T_2## based on the arrangement of the ropes shown in the diagram?
Once found:

$$m = \frac{T_1 + T_2 + N_A}{g}$$

Update: I tried finding ##T_2## by first noting that the tension throughout the string from B to the ceiling is 76 N. Applying the equilibrium condition for the two pulleys with strings directly attached to the triangular support to which the rope in question is attached. We now have ##T_2 = 4T_1##.
Is this correct?
 

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  • #2
MohammedRady97 said:

Homework Statement



A former student of mechanics wishes to weigh himself but has access only to a scale A with capacity limited to 400 N and a small 80 N spring dynamometer B. With the rig shown he discovers that when he exerts a pull on the rope so that B registers 76 N, the scale A reads 268 N. What is his mass ##m##? Also, what range of weight could be measured by this system?

Homework Equations



Since the student is in equilibrium:

$$\sum F_y = 0$$

The Attempt at a Solution



The normal reaction acting on the student is 268 N. There are two tensions acting on the student; ##T_1## and ##T_2## (see diagram).
##T_1## is clearly 76 N. However, I can't seem to find ##T_2##. How do I assign a value to ##T_2## based on the arrangement of the ropes shown in the diagram?
Once found:

$$m = \frac{T_1 + T_2 + N_A}{g}$$

Update: I tried finding ##T_2## by first noting that the tension throughout the string from B to the ceiling is 76 N. Applying the equilibrium condition for the two pulleys with strings directly attached to the triangular support to which the rope in question is attached. We now have ##T_2 = 4T_1##.
Is this correct?
Yes, T2 = 4T1
 

What is a 400 N Scale and 80 N Spring Dynamometer?

A 400 N Scale and 80 N Spring Dynamometer is a type of scientific equipment used to measure the weight or force of an object. The scale has a maximum weight capacity of 400 Newtons, while the spring dynamometer can measure up to 80 Newtons of force.

How does a 400 N Scale and 80 N Spring Dynamometer work?

The scale and dynamometer work together using the principle of Hooke's law, which states that the force needed to extend or compress a spring is directly proportional to the distance the spring is extended or compressed. The scale measures the weight of the object by the amount of force it exerts on the spring, and the dynamometer measures the amount of force being applied to the spring.

What are the units of measurement for a 400 N Scale and 80 N Spring Dynamometer?

The units of measurement for the scale and dynamometer are in Newtons (N), which is a unit of force in the International System of Units (SI). The scale measures weight in Newtons, while the dynamometer measures force in Newtons.

What are the potential sources of error when using a 400 N Scale and 80 N Spring Dynamometer?

Some potential sources of error when using this equipment include human error in reading the measurements, variations in the spring's tension over time, and external factors such as air resistance or friction between the object and the scale. It is important to calibrate the equipment regularly and take multiple measurements to reduce errors.

What are the applications of a 400 N Scale and 80 N Spring Dynamometer?

This type of equipment is commonly used in physics and engineering experiments, as well as in industries such as manufacturing and construction. It can also be used in educational settings to teach about forces and measurement techniques.

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