Download U3H1 Problem Sheet 1 - Baltimore Polytechnic Institute

Baltimore Polytechnic Institute
Unit 3: Engineering Design
Engineering Practicum
Problem Sheet #1:
Force, Energy, Work, Power, and Efficiency
Definitions:
a.
Force – a push, pull, or twist; it is a vector quantity; N, lbf
b.
Newton’s Laws of Motion – inertia; Fnet = m x a; reciprocal actions
c.
Energy – the amount of work that is or can be performed by a force; 1st law of thermodynamics
d.
Potential Energy – stored energy (PEgrav = mgh)
e.
Kinetic Energy – energy an object has due to motion (KE = ½mv2)
f.
Work – “the amount of energy transferred to a system by a force acting through a distance”; the change in kinetic energy
of a system; W = F x d
g.
Power – the rate of change of work or energy; P = W / t
h.
Efficiency – the ratio of the energy delivered by a system to the energy supplied to it; 2nd law of thermodynamics;
Eff = (Output/Input) x 100%
i.
Engineering Problem Solving Process – 1) Write Given, Assign Variables, Sketch and Label Diagram;
2) Write Formulas / Equations; 3) Substitute and Solve; 4) Check Answer, THEN Box Answer
1.
For the following word problems, follow all problem solving steps (include a free-body diagram in each solution).
a.
b.
A 105 gram hockey puck is sliding across the ice. A
c.
A forklift raises a box from the ground to a height of 7
player exerts a constant 4.5 Newton force over a
feet; the forklift does 3,500 ft-lbs of work. How much
distance of 0.15 meter. How much work does the
does the box weigh? What is the change in potential
player do on the puck?
energy of the box?
A mechanical engineer lifts a box of gears that
d.
A 2-kg ball falls 11 m. How much work does the force of
weighs 65 pounds. The box is lifted 2.5 feet. How
gravity do on the ball? How fast is the ball falling when
much word does the engineer do on the box?
it hits the ground?
Baltimore Polytechnic Institute
2.
Unit 3: Engineering Design
Engineering Practicum
A rope is used to pull a metal box 15 m across the floor in 34 seconds. The rope is held at an angle of 45o with the floor and a
force of 628 N is used. How much work does the force on the rope do? How much power is consumed?
3.
A sailor pulls a boat 90 feet along a dock using a rope that makes a 30o angle with the horizontal. It takes the sailor 75
seconds to pull the boat that distance. How much work does the sailor do on the boat if he exerts a force of 57 pounds? How
efficiently is the force being applied at this angle? How much power is needed?
4.
A 1380-kg car is sitting on a hill in neutral. The angle the hill makes with the horizontal is 30 o. The distance from flat ground
to the car is 200 m. What is the potential energy of the car? How efficient is the force of gravity being applied to the vehicle?
What is the work done on the car by gravity? What is the kinetic energy of the car when it reaches the bottom of the hill?
What is the velocity of the car when it reaches the bottom of the hill?