9. Work & Energy

Intro to Energy & Kinetic Energy

Multiple Choice
About 50,000 years ago, a meteor crashed into the earth near present-day Flagstaff, Arizona. Some estimates suggest this meteor had a mass of about 1.4×10⁸ kg and released 1×10¹⁶ J of energy when it slammed into the Earth. Calculate the approximate speed of this meteor before impact.
Multiple Choice
A particle with mass m and velocity v has kinetic energy K. What is the kinetic energy of a particle with mass m/2 and velocity 2v?
Multiple Choice
Block A has mass $20 kg$ and block B has mass $50 kg$ . Starting from rest, the two blocks are pushed by identical forces through a distance of $10 m$ . Which block (if either) is going faster at end of the $10 m$ ? Which block (if either) has the greatest kinetic energy at the end of the $10 m$ ?
Multiple Choice
What is the kinetic energy of a $500 kg$ car traveling at $27 m / s$ (about $60 mph$ )?
Open Question
(II) For a satellite of mass in a circular orbit of radius r_S around the Earth, determine
(a) its kinetic energy K
Open Question
(c) Is it reasonable that a 30-kg child could run fast enough to have 100 J of kinetic energy?
Open Question
(I) At room temperature, an oxygen molecule, with mass of 5.31 x 10⁻²⁶ kg, typically has a kinetic energy of about 6.21 x 10⁻²¹ J . How fast is it moving?
Open Question
A mother has four times the mass of her young son. Both are running with the same kinetic energy. What is the ratio v(son)/v(mother) of their speeds?
Open Question
At what speed does a 1000 kg compact car have the same kinetic energy as a 20,000 kg truck going 25 km/h?
Open Question
A 45 g bug is hovering in the air. A gust of wind exerts a force F (→ above F) = (4.0î-6.0ĵ) x 10¯² N on the bug. (b) What is the bug's speed at the end of this displacement? Assume that the speed is due entirely to the wind.
Open Question
How much work does tension do to pull the mass from the bottom of the hill (θ = 0) to the top at constant speed? To answer this question, write an expression for the work done when the mass moves through a very small distance ds while it has angle θ, replace ds with an equivalent expression involving R and dθ , then integrate.
Open Question
A Porsche 944 Turbo has a rated engine power of 217 hp. 30% of the power is lost in the engine and the drive train, and 70% reaches the wheels. The total mass of the car and driver is 1480 kg, and two-thirds of the weight is over the drive wheels. (c) How long does it take the Porsche to reach the maximum power output?
Open Question
A Porsche 944 Turbo has a rated engine power of 217 hp. 30% of the power is lost in the engine and the drive train, and 70% reaches the wheels. The total mass of the car and driver is 1480 kg, and two-thirds of the weight is over the drive wheels. (b) If the Porsche accelerates at aₘₐₓ, what is its speed when it reaches maximum power output?
Open Question
A Porsche 944 Turbo has a rated engine power of 217 hp. 30% of the power is lost in the engine and the drive train, and 70%reaches the wheels. The total mass of the car and driver is 1480 kg, and two-thirds of the weight is over the drive wheels. (a) What is the maximum acceleration of the Porsche on a concrete surface where μₛ = 1.00 ? Hint: What force pushes the car forward?
Open Question
A 150 g particle at x = 0 is moving at 2.00 m/s in the + x - direction. As it moves, it experiences a force given by Fₓ = (0.250 N) sin (x/2.00 m) . What is the particle's speed when it reaches x = 3.14 m ?