Q: A person uses a ramp to load a 1200 N motorcycle onto a truck bed 1.3 m high by pushing it up a 2.4 m ramp with an effort force of 820 N. What is the efficiency of the ramp?

$$\eta = \frac{W_{out}}{W_{in}} \times 100 = \frac{(1200)(1.3)}{(820)(2.4)} \times 100 = 79\%$$

Q: A 1.0 \times $$10^3$$ \ kg$ object is lifted 5.0 m in 12.0 s by a 5.0 kW crane. What is the efficiency of the crane?

$$\eta = \frac{W_{out}}{W_{in}} \times 100 = \frac{(1000)(9.8)(5.0)}{5000 \times 12.0} \times 100 = 82\%$$

Question 1

A person uses a ramp to load a 1200 N motorcycle onto a truck bed 1.3 m high by pushing it up a 2.4 m ramp with an effort force of 820 N. What is the efficiency of the ramp?

Accepted Answer

$$\eta = \frac{W_{out}}{W_{in}} 	imes 100 = \frac{(1200)(1.3)}{(820)(2.4)} 	imes 100 = 79\%$$

Question 2

Which of the following best describes the function of a wedge as a simple machine?

Accepted Answer

It converts an input force into two output forces that push materials apart.

Question 3

A 1.0 	imes $$10^3$$ \ kg$ object is lifted 5.0 m in 12.0 s by a 5.0 kW crane. What is the efficiency of the crane?

Accepted Answer

$$\eta = \frac{W_{out}}{W_{in}} 	imes 100 = \frac{(1000)(9.8)(5.0)}{5000 	imes 12.0} 	imes 100 = 82\%$$

Question 4

Which equation correctly defines the mechanical advantage (MA) of a simple machine?

Accepted Answer

$$MA = \frac{F_{r}}{F_{e}}$$

Question 5

A lever has a resistance arm of 3.0 m and an effort arm of 12 cm. What is the ideal mechanical advantage (IMA) of the lever?

Accepted Answer

$$IMA = \frac{d_{e}}{d_{r}} = \frac{0.12}{3.0} = 0.04$$

Question 6

You exert a force of 2800 N to lift a desk onto a porch. Using a ramp, you only need 1400 N. What is the mechanical advantage of the ramp?

Accepted Answer

$$MA = \frac{2800}{1400} = 2$$

Question 7

A 15.0 kg crate is lifted 10.0 cm using a pulley system. If a 95.0 N force is applied over 20.0 cm, what is the mechanical advantage (MA)? (Assume $$g = 9.8 \ m/s^2$)

Accepted Answer

$$MA = \frac{F_{r}}{F_{e}} = \frac{(15.0)(9.8)}{95.0} = 1.55$$

Question 8

Which of the following statements about simple machines is correct?

Accepted Answer

Simple machines decrease the input force required but increase the distance over which the force is applied.

Question 9

A wheel and axle system has a wheel radius of 0.5 m and an axle radius of 0.1 m. What is the ideal mechanical advantage (IMA)?

Accepted Answer

$$IMA = \frac{R}{r} = \frac{0.5}{0.1} = 5$$

Question 10

If a pulley system has 4 supporting ropes, what is its ideal mechanical advantage (IMA)?

Accepted Answer

$$IMA = 4$$

Question 11

A 50.0 N load is placed 1.0 m from the fulcrum of a lever. You apply a 75 N force 5.0 m from the fulcrum. What is the mechanical advantage (MA)?

Accepted Answer

$$MA = \frac{F_{r}}{F_{e}} = \frac{50.0}{75.0} = 0.67$$

Question 12

Which of the following best explains why a screw is considered a simple machine?

Accepted Answer

It converts rotational input force into linear output force over a distance equal to the pitch.

Question 13

A hammer is used to pull a nail out of wood, as shown in the image. What type of simple machine is the hammer acting as?

Accepted Answer

A lever

Question 14

Which of the following is NOT a type of simple machine?

Accepted Answer

Gear

Question 15

If a machine has an efficiency of 100%, which of the following must be true?

Accepted Answer

All input work is converted to output work with no energy lost to friction or heat.

Question 16

A person uses a wheel and axle to lift a bucket from a well. If the effort is applied to a wheel of radius 0.4 m and the axle has a radius of 0.1 m, what is the ideal mechanical advantage?

Accepted Answer

$$IMA = \frac{0.4}{0.1} = 4$$

Question 17

Which of the following best describes the trade-off when using a simple machine to make a task easier?

Accepted Answer

The input force decreases, but the distance over which the force is applied increases.

Physics Study Guide: Simple Machines, Mechanical Advantage, and Efficiency

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