9.5 Simple machines  (Page 4/5)

Why are the forces exerted on the outside world by the limbs of our bodies usually much smaller than the forces exerted by muscles inside the body?

Explain why the forces in our joints are several times larger than the forces we exert on the outside world with our limbs. Can these forces be even greater than muscle forces (see previous Question)?

What is the mechanical advantage of a nail puller—similar to the one shown in [link] —where you exert a force $\text{45 cm}$ from the pivot and the nail is $\text{1.8 cm}$ on the other side? What minimum force must you exert to apply a force of $\text{1250 N}$ to the nail?

Suppose you needed to raise a 250-kg mower a distance of 6.0 cm above the ground to change a tire. If you had a 2.0-m long lever, where would you place the fulcrum if your force was limited to 300 N?

a) What is the mechanical advantage of a wheelbarrow, such as the one in [link] , if the center of gravity of the wheelbarrow and its load has a perpendicular lever arm of 5.50 cm, while the hands have a perpendicular lever arm of 1.02 m? (b) What upward force should you exert to support the wheelbarrow and its load if their combined mass is 55.0 kg? (c) What force does the wheel exert on the ground?

A typical car has an axle with $1\text{.}\text{10 cm}$ radius driving a tire with a radius of $\text{27}\text{.5 cm}$ . What is its mechanical advantage assuming the very simplified model in [link] (b)?

What force does the nail puller in [link] exert on the supporting surface? The nail puller has a mass of 2.10 kg.

If you used an ideal pulley of the type shown in [link] (a) to support a car engine of mass $\text{115 kg}$ , (a) What would be the tension in the rope? (b) What force must the ceiling supply, assuming you pull straight down on the rope? Neglect the pulley system's mass.

Repeat [link] for the pulley shown in [link] (c), assuming you pull straight up on the rope. The pulley system's mass is $\text{7.00 kg}$ .

As a young student, you likely learned that simple machines are capable of increasing the ability to lift and move objects. Now, as an educated AP Physics student, you are aware that this capability is governed by the relationship between force and torque.

In the space below, explain why torque is integral to the increase in force created by a simple machine. You may use an example or diagram to assist in your explanation. Be sure to cite the mechanical advantage in your explanation as well.

Figure 9.24(a) shows a wheelbarrow being lifted by an applied force F _i . If the wheelbarrow is filled with twenty bricks massing 3 kg each, estimate the value of the applied force F _i . Provide an explanation behind the total weight w and any reasoning toward your final answer. Additionally, provide a range of values over which you feel the force could exist.