Question

Supppose you pull a sled with a rope that makes an angle of ${30.0}^{\circ }$ to the horizontal. How much work do you do if you pull with $25.0\mathrm{N}$ of force and the sled moves $25.0\mathrm{m}?$

Short answer

Question: Calculate the work done by a person pulling a sled with a force of 25 N at an angle of 30 degrees above the horizontal for a distance of 25 meters. Answer: The work done in pulling the sled is approximately 541.2 joules.

Step-by-step solution

Convert the angle to radians

Converting the given angle from degrees to radians using the formula radians=$\frac{(degrees)(\pi )}{180}$: Angle = $\frac{30.0\times \pi }{180}=\frac{\pi }{6}$ radians.

Calculate the horizontal component of the force

The horizontal component of the force can be calculated by multiplying the force with the cosine of the angle as follows: Horizontal Force = Force × cos(angle) Horizontal Force = $25.0N\times \cos (\frac{\pi }{6})$

Calculate the work done by the horizontal component of the force

The work done can be calculated by multiplying the horizontal component of the force with the distance as follows: Work = Horizontal Force × Distance Work = $(25.0N\times \cos (\frac{\pi }{6}))\times 25.0m$

Calculate the final result

Evaluate the expression to find the work done: Work = $(25.0N\times \cos (\frac{\pi }{6}))\times 25.0m\approx 541.2J$ The work done in pulling the sled is approximately 541.2 joules.

Key concepts

Calculating Work in Physics

The concept of work in physics is fundamental to understanding how energy is transferred by a force moving an object. Work is calculated as the product of the force applied to an object and the distance over which it is applied. But it's not as simple as multiplying any force by any distance. The force must be in the direction of the movement. The equation to remember is: $$W=F\times d\times \cos (\theta )$$, where $W$ is work, $F$ is the magnitude of the force, $d$ is the distance moved by the object, and $\theta$ is the angle between the direction of the force and the direction of the movement.

Knowing this equation, we see that only the component of force that acts in the direction of motion does actual work on the object. If the force is perpendicular to the displacement (like lifting a weight vertically while walking forward), the work done in the direction of displacement is zero. While it may seem complex, understanding this formula enables you to solve a wide array of problems in physics.

Horizontal Component of Force

When a force is applied at an angle, not all of that force is effective in moving an object along the horizontal. The horizontal component of the applied force is what does work in moving an object horizontally. The horizontal force is found by multiplying the total force by the cosine of the angle of application: $$F_x=F\times \cos (\theta )$$, where $F_x$ is the horizontal force, $F$ is the applied force, and $\theta$ is the angle. The angle's cosine effectively 'scales down' the force to its horizontal component.

It's crucial to understand the horizontal component of force because this is precisely the part that does the work when an object moves horizontally. Having the ability to sort which portion of the force is contributing to the work done prevents misconceptions about the efficiency and energy requirements of tasks.

Angle Conversion to Radians

Angles can be measured in degrees or radians, and it's important in physics to be able to convert from one to the other. Radians are a 'natural' unit of angular measure in mathematics and physics because they relate the arc length directly to the radius of a circle. To convert degrees to radians, we use the conversion factor $\frac{\pi \text{ radians}}{{180}^{\circ }}$. The conversion formula is $$\text{radians}=\frac{(\text{degrees})(\pi )}{180}$$.

In physics exercises like calculating work, forces or motions on paths that involve circular arcs, and many other applications, radians are essential. Moreover, trigonometric functions in calculators are often set to use radians, and using the incorrect unit could lead to errors in calculations.

Force-Distance Relationship

In the context of work, the force-distance relationship refers to how the work done is dependent on both the magnitude of the force applied and the distance over which it is applied. The core concept here is that both factors — force and distance — are equally important. An increased force on an object over the same distance results in more work done, and similarly, applying a force over a greater distance also increases the work. The work's dependence on distance is linear, which means that doubling the distance will double the work done, as long as the force remains constant. This relationship is captured in the work equation: $$W=F\times d$$, which simplifies the general expression $W=F\times d\times \cos (\theta )$ when the force is applied in the direction of motion ($\theta =0^{\circ }$).

Understanding the force-distance relationship helps in analyzing systems' energy requirements and designing systems in engineering, from simple pulleys to complex machines.