- On a first-class lever like a seesaw, moving the fulcrum closer to the load (resistance) will
Answer: decrease the effort needed but increase the distance the effort must be applied.
Moving the fulcrum closer to the load shortens the resistance arm and lengthens the effort arm. This increases the lever's mechanical advantage (MA = Effort Arm / Resistance Arm), which means less effort is needed to move the load. The trade-off is that the effort must be applied over a proportionally greater distance.
- A screwdriver with a thick handle is generally easier to use for turning a tight screw than one with a thin handle. The primary mechanical reason for this is that the thick handle
Answer: increases the mechanical advantage.
A screwdriver functions as a wheel and axle. The handle is the 'wheel' and the shaft is the 'axle'. A larger radius for the wheel (the thick handle) increases the mechanical advantage. This means a given amount of effort force applied to the handle results in a greater turning force (torque) at the screw.
- A metal spoon and a wooden spoon are both placed in a cup of hot coffee. After one minute, which spoon's handle will feel hotter to the touch?
Answer: The metal spoon
This question tests heat transfer by conduction. Metal is an excellent thermal conductor, meaning it transfers heat quickly. Wood is a thermal insulator, meaning it transfers heat slowly. Therefore, heat will travel up the handle of the metal spoon much faster, making it feel hotter.
- A single fixed pulley is used to lift a 50-pound box. Ignoring friction, how much effort force is required to lift the box?
Answer: 50 pounds
A single fixed pulley provides no mechanical advantage; its purpose is to change the direction of the force. Therefore, the effort required to lift the load is equal to the weight of the load, which is 50 pounds.
- When a rifle fires a bullet, the rifle recoils backward. This backward movement is a direct result of the principle of
Answer: conservation of momentum.
This is an example of Newton's Third Law and the conservation of momentum. The total momentum of the rifle-bullet system is zero before firing. To keep the total momentum zero after firing, the forward momentum of the bullet must be balanced by an equal and opposite backward momentum of the rifle, causing it to recoil.
- A weight is tied to a string and swung in a horizontal circle at a constant speed. If the string breaks, the weight will most likely
Answer: fly off in a straight line tangent to the circle.
The tension in the string provides the centripetal force required to keep the weight moving in a circle. When the string breaks, this force disappears. Due to inertia, the weight will continue to move in a straight line in the direction it was going at the moment the string broke, which is tangent to the circular path.
- A block of wood and a block of steel of the exact same volume are fully submerged in a tank of water. The buoyant force is
Answer: the same on both blocks.
According to Archimedes' principle, the buoyant force on a submerged object is equal to the weight of the fluid it displaces. Since both blocks have the same volume, they displace the same volume of water. Therefore, they experience the same buoyant force, regardless of their own weight or density.
- If a machine performs 600 foot-pounds of work in 3 seconds, what is its power output?
Answer: 200 foot-pounds per second
Power is the rate at which work is done. It is calculated as Power = Work ÷ Time. In this case, Power = 600 ft-lbs ÷ 3 s = 200 ft-lbs/s.
- A bimetallic strip is made of brass and steel bonded together side-by-side. Brass expands more than steel when heated. If the straight strip is heated, it will
Answer: bend with the brass on the outside of the curve.
When heated, both metals expand. Since brass expands more, the brass side will become longer than the steel side. To accommodate this difference in length while being bonded, the strip must curve. The longer material (brass) will form the outer side of the curve, which has a larger radius.
- In a simple hydraulic lift, a small force applied to a small piston lifts a heavy object on a large piston. This principle works because the
Answer: force is multiplied due to the pressure being constant throughout the fluid.
This demonstrates Pascal's Principle, which states that pressure applied to an enclosed, incompressible fluid is transmitted equally throughout the fluid. Since Pressure = Force/Area, a small force on a small area creates the same pressure as a large force on a large area (F₁/A₁ = F₂/A₂). This allows for force multiplication.
- A driving gear with 40 teeth is connected to a driven gear with 20 teeth. If the driving gear makes 100 revolutions per minute (RPM), what is the speed of the driven gear?
Answer: 200 RPM
The gear ratio determines the speed relationship. The formula is (Teeth₁ × Speed₁) = (Teeth₂ × Speed₂). So, (40 teeth × 100 RPM) = (20 teeth × Speed₂). This simplifies to 4000 = 20 × Speed₂, and solving for Speed₂ gives 4000 ÷ 20 = 200 RPM. The smaller gear spins faster.
- A force of 10 newtons is required to stretch a certain spring by 2 centimeters. Assuming the spring obeys Hooke's Law, what force is required to stretch it by 6 centimeters?
Answer: 30 newtons
Hooke's Law states that the force needed to stretch or compress a spring by some distance is directly proportional to that distance (F = kx). Since the distance is tripled (from 2 cm to 6 cm), the required force will also be tripled. Therefore, the new force is 10 newtons × 3 = 30 newtons.
- Three gears are arranged in a line so that the first gear meshes with the second, and the second gear meshes with the third. If the first gear rotates clockwise, what is the direction of rotation for the third gear?
Answer: Clockwise
Meshed gears always turn in opposite directions. If the first gear turns clockwise, the second gear it meshes with will turn counter-clockwise. Since the second gear (counter-clockwise) meshes with the third, the third gear will turn clockwise.
- Pushing a heavy box up a long, gentle ramp to a certain height requires less force than lifting it straight up. The trade-off is that
Answer: the force must be applied over a greater distance.
An inclined plane is a simple machine that provides mechanical advantage. It allows you to use less force to lift an object, but you must apply that force over a longer distance. The total work done against gravity remains the same.
- Two identical containers are filled to the same height, one with freshwater and one with saltwater. At the bottom of the containers, the pressure is
Answer: greater in the saltwater container.
Fluid pressure at a certain depth depends on the height, gravity, and density of the fluid (P = ρgh). Because saltwater is denser than freshwater, it will exert more pressure at the same depth.
- To loosen a very tight bolt with a wrench, a person should apply force
Answer: at the end of the wrench handle, farthest from the bolt.
This question relates to torque, which is the rotational force needed to turn an object. Torque is calculated as Force × Lever Arm. To maximize the torque for a given amount of force, you must maximize the length of the lever arm, which is the distance from the pivot point (the bolt) to where the force is applied.
- A rock resting at the edge of a cliff has its maximum amount of
Answer: potential energy.
Potential energy is the stored energy an object has due to its position. At the highest point before it begins to fall, the rock has its maximum gravitational potential energy. This energy is converted to kinetic energy (the energy of motion) as it falls.
- If the air pressure in a tire is 32 pounds per square inch (psi), what is the total force exerted on an internal patch that covers an area of 4 square inches?
Answer: 128 pounds
The relationship between pressure, force, and area is given by the formula Pressure = Force ÷ Area. To find the force, you rearrange the formula to Force = Pressure × Area. In this case, Force = 32 psi × 4 sq in = 128 pounds.
- A crowbar is used to lift a 200-pound rock. The fulcrum is 6 inches from the rock, and force is applied 30 inches from the fulcrum. What is the mechanical advantage of the crowbar?
Answer: 5
The mechanical advantage (MA) of a lever is calculated by dividing the length of the effort arm by the length of the resistance arm. Here, the effort arm is 30 inches and the resistance arm is 6 inches. Therefore, MA = 30 ÷ 6 = 5.
- It is generally harder to start pushing a heavy crate from a standstill than it is to keep it sliding. This is because
Answer: static friction is greater than kinetic friction.
Static friction is the frictional force that prevents an object from moving when a force is applied. Kinetic (or sliding) friction is the force that opposes motion once the object is already moving. For most surfaces, the force of static friction is greater than the force of kinetic friction.
