# Solving Torque & Forces: Bicyclist w/ 71 kg Weight

• ibrahim1996
In summary, In summary, the conversation is about a person struggling with understanding torque and asking for help with a specific problem involving a bicyclist weighing 71 kg and the torque generated by a pedal arm at different angles. The summary also mentions the questions asked and suggests methods for solving them.
ibrahim1996
Hey, I've tried working on this and I just cannot figure it out. I went to someone for help and they got confused. Can someone please SHOW ME how it is done. I prefer to see step by step so I know where I went wrong.

Thanks,

A bicyclist weighing 71 kg starts his ride by putting all his weight on one pedal. The pedal arm is
15 cm long and is initially positioned up at an angle of 31° from the perpendicular.

a. Sketch the pedal and draw the forces acting on it. Calculate the torque initially generated by
the rider.
b. Under the same conditions, how much torque is generated if the pedal arm is horizontal?
c. The material of the pedal arms is only rated for a maximum torque of 250 Nm. What is the
maximum weight of a rider that this bicycle can withstand?

ibrahim1996 said:
Hey, I've tried working on this and I just cannot figure it out. I went to someone for help and they got confused. Can someone please SHOW ME how it is done. I prefer to see step by step so I know where I went wrong.

Thanks,

A bicyclist weighing 71 kg starts his ride by putting all his weight on one pedal. The pedal arm is
15 cm long and is initially positioned up at an angle of 31° from the perpendicular.

a. Sketch the pedal and draw the forces acting on it. Calculate the torque initially generated by
the rider.
Have you drawn the picture? Do you know that torque is "force perpendicular to the length of the lever". Here, the rider is putting all his weight vertically so you need to mulltiply that by the horizontal component of the length of the pedal arm.

b. Under the same conditions, how much torque is generated if the pedal arm is horizontal?
This is easier than (a). Do you see why?

c. The material of the pedal arms is only rated for a maximum torque of 250 Nm. What is the maximum weight of a rider that this bicycle can withstand?
The maximum torque for a given weight occurs when the pedal arm is horizontal (part b). Do you see why? Set the length of the pedal arm, times the unknown weight, equal to 250 and solve for the weight.

## 1. What is torque?

Torque is a measure of the force that causes an object to rotate around an axis or pivot point. It is calculated by multiplying the force applied to an object by the distance from the axis of rotation to the point where the force is applied.

## 2. How is torque related to forces?

Torque and forces are closely related, as forces can cause an object to rotate and thus create torque. A force applied at a perpendicular distance from an object's axis of rotation will generate torque.

## 3. How does weight affect torque in a bicyclist?

In the context of a bicyclist, weight affects torque by increasing the force applied to the pedals. A heavier bicyclist will produce more torque than a lighter one, assuming everything else is equal.

## 4. What other factors besides weight can affect torque in a bicyclist?

Other factors that can affect torque in a bicyclist include the gear ratio, the length of the crank arm, and the force applied to the pedals. The angle of the bicycle's incline can also affect the torque needed to maintain a constant speed.

## 5. How can torque be increased or decreased in a bicyclist?

To increase torque, a bicyclist can increase the force applied to the pedals, increase the gear ratio, or increase the length of the crank arm. To decrease torque, a bicyclist can do the opposite - decrease the force applied, decrease the gear ratio, or decrease the length of the crank arm.

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