Question 1

A car traveling at 65 mph suddenly skids to a stop due to traffic congestion. Where does the car's kinetic energy go?

Accepted Answer

Some of it is transformed to internal energy and some of it is transferred away by mechanical waves.

Question 2

A stone is launched upward and is subject to both gravity and air resistance. How does the time to reach the top of its flight path compare to the time to return from the top to its original position?

Accepted Answer

The time to reach the top is smaller than the time to return.

Question 3

A cart on an air track is moving at $$0.5\ \mathrm{m/s}$$ when the air is suddenly turned off. The cart comes to rest after traveling $$1\ \mathrm{m}. If $$the experiment is repeated with the cart moving at $$1\ \mathrm{m/s}$$ when the air is turned off, how far does the cart travel before coming to rest?

Accepted Answer

$$2\ \mathrm{m}$$

Question 4

A crate slides down a rough ramp (Earth-crate-ramp as an isolated system). If the crate starts from rest at height $$h$$ and the coefficient of kinetic friction is $$\mu_k$$, what is the speed $$v_f at $$the bottom?

Accepted Answer

$$v_f = \sqrt{2gh - 2\mu_k f d}$$

Question 5

A block of mass $$m is $$given an initial velocity $$v_0$$ and collides with a spring (block-spring-surface as isolated system). If friction is present, which equation describes the mechanical energy loss?

Accepted Answer

$$\Delta K + \Delta U = -f_k d$$

Question 6

A system of connected blocks is released from rest when the spring is unstretched. If the hanging block falls a distance $$d$$, what is the coefficient of kinetic friction $$\mu_k$$?

Accepted Answer

$$\mu_k = \frac{m_h}{m_g} - \frac{k x^2$}{2 m_g g d}$$

Question 7

A tow rope pulls a skier up the slope at constant speed. What energy transfer(s) is taking place?

Accepted Answer

Both A and B

Question 8

How much work is done by the environment in the process represented by the energy bar chart below? (Assume the chart shows a decrease in kinetic energy and an increase in internal energy by 2 J.)

Accepted Answer

$$2\ \mathrm{J}$$

Question 9

For a non-isolated system involving both nonconservative and conservative forces, which equation correctly relates work and energy changes?

Accepted Answer

$$W = \Delta E_{\mathrm{system}} = \Delta E_{\mathrm{mech}} + \Delta E_{\mathrm{int}} 
eq 0$$

Question 10

A block is pulled by a constant force $$F$$ over a rough horizontal surface. If the coefficient of kinetic friction is $$\mu_k$$, what is the work done by friction after the block moves a distance $$d$$?

Accepted Answer

$$W_{\mathrm{fric}} = \mu_k m g d$$

Question 11

A block is pulled at an angle $$	heta$$ over a rough surface. If the force involved in work is reduced, what happens to the friction force and the final speed?

Accepted Answer

Friction force is reduced and final speed is zero.

Question 12

A block is attached to a spring and pulled across a rough surface. If the spring is stretched a distance $$x$$ and the block moves a distance $$d$$, what is the equation for the work done by the spring and friction?

Accepted Answer

$$W = \frac{1}{2} k x^2$ - \mu_k m g d$$

Question 13

Which student has the largest power output when running up the stairs, given the same vertical height but different times?

Accepted Answer

The student who takes the shortest time.

Question 14

Which equation defines instantaneous power?

Accepted Answer

$$P = \frac{dE}{dt}$$

Question 15

What is the SI unit of power and its equivalent in base units?

Accepted Answer

Watt ($$\mathrm{W}$$), $$1\ \mathrm{W} = 1\ \mathrm{kg} \cdot \mathrm{m}^2 / \mathrm{s}^3$$

Question 16

An elevator moves up at constant speed $$v. If $$the tension in the cable is $$T$$ and the elevator's weight is $$Mg$$, what is the power delivered by the motor?

Accepted Answer

$$P = T \cdot v$$

Question 17

A 3.0 kg mass falls 1.5 m in a two-mass system. If the frictional force on the 2.0 kg mass is 2.4 N, what is the mechanical energy done by friction?

Accepted Answer

$$-3.6\ \mathrm{J}$$

Question 18

A 1.2 kg projectile is launched vertically at 20 m/s. At its maximum height, air resistance has done $$-24\ \mathrm{J} of $$work. What is the change in mechanical energy caused by air resistance?

Accepted Answer

$$-24\ \mathrm{J}$$

Question 19

A block is released from rest when a spring is stretched a distance $$x. If$$ $$k = 50\ \mathrm{N/m}$$, $$x = 0.30\ \mathrm{m}$$, $$m = 0.42\ \mathrm{kg}$$, and $$\mu_k = 0.25$$, what is the speed of the block when it passes through the position where the spring is unstretched?

Accepted Answer

$$0.71\ \mathrm{m/s}$$

Energy, Work, and Power in Mechanical Systems: Study Notes

스터디 가이드 - 연습 문제

학습 가이드 - 플래시카드