Q: A 1200 kg car rounds a flat curve of radius $$90.0\ \mathrm{m}$$ with a coefficient of friction $$\mu = 0.65. $$What is the maximum speed the car can have without skidding?

$$v_{\text{max}} = \sqrt{\mu g r}$$

Q: A force $$\vec{F} = (100\hat{i} + 9.0\hat{j} + 120\hat{k})\ \mathrm{kN}$$ acts on an object displaced by $$\vec{d} = (5.0\hat{i} + 4.0\hat{j})\ \mathrm{m}. $$What is the work done by the force?

$$W = \vec{F} \cdot \vec{d} = 100 \times 5.0 + 9.0 \times 4.0 = 500 + 36 = 536\ \mathrm{kJ}$$

Q: Which equation best represents the conservation of mechanical energy for a system with friction?

$$K_i + U_i = K_f + U_f + E_{\text{thermal}}$$

Question 1

Which of the following is a correct example of a non-conservative force?

Accepted Answer

Frictional force

Question 2

A block of mass $$m = 7\ \mathrm{kg}$$ slides down a frictionless plane inclined at $$	heta = 22^\circ to $$the horizontal. What is the acceleration of the block?

Accepted Answer

$$a = g \sin 22^\circ$$

Question 3

Which of Newton's laws explains why passengers move forward when a car suddenly stops?

Accepted Answer

Newton's First Law (Law of Inertia)

Question 4

A 1200 kg car rounds a flat curve of radius $$90.0\ \mathrm{m}$$ with a coefficient of friction $$\mu = 0.65. $$What is the maximum speed the car can have without skidding?

Accepted Answer

$$v_{	ext{max}} = \sqrt{\mu g r}$$

Question 5

A child of mass $$22.5\ \mathrm{kg}$$ sits $$1.40\ \mathrm{m}$$ from the center of a merry-go-round moving at $$1.30\ \mathrm{m/s}. $$What is the net horizontal force exerted on the child?

Accepted Answer

$$F = m \dfrac{v^2$}{r}$$

Question 6

Two satellites orbit Earth at altitudes of $$8500\ \mathrm{km}$$ and $$7000\ \mathrm{km}$$ above the surface. Which satellite moves faster and by what factor?

Accepted Answer

The satellite at $$7000\ \mathrm{km}$$ moves faster by a factor $$\sqrt{\dfrac{r_2$}{r_1$}}$$

Question 7

Which of the following is NOT a fundamental force recognized by modern physics?

Accepted Answer

Friction

Question 8

A force $$\vec{F} = (100\hat{i} + 9.0\hat{j} + 120\hat{k})\ \mathrm{kN}$$ acts on an object displaced by $$\vec{d} = (5.0\hat{i} + 4.0\hat{j})\ \mathrm{m}. $$What is the work done by the force?

Accepted Answer

$$W = \vec{F} \cdot \vec{d} = 100 	imes 5.0 + 9.0 	imes 4.0 = 500 + 36 = 536\ \mathrm{kJ}$$

Question 9

A vertical spring with $$k = 875\ \mathrm{N/m} is $$compressed $$0.220\ \mathrm{m} by a$$ $$0.380\ \mathrm{kg}$$ ball. What is the upward speed of the ball when released?

Accepted Answer

$$v = \sqrt{\dfrac{k x^2$}{m}}$$

Question 10

Which equation best represents the conservation of mechanical energy for a system with friction?

Accepted Answer

$$K_i + U_i = K_f + U_f + E_{	ext{thermal}}$$

Question 11

An $$80\ \mathrm{kg}$$ mass is $$1.5\ \mathrm{m}$$ above the ground and compresses a spring $$0.1\ \mathrm{m}$$ with $$k = 5.2\ \mathrm{kN/m}. $$What is the total potential energy?

Accepted Answer

$$U = mgh + \dfrac{1}{2} k x^2$

Question 12

A NASA satellite observes an asteroid of mass $$4 	imes 10^9$\ \mathrm{kg}$$ approaching Earth at $$660\ \mathrm{m/s}$$ from $$5.0 	imes 10^8$\ \mathrm{km}$$ away. Neglecting atmospheric friction, what principle is used to determine its impact speed?

Accepted Answer

Conservation of energy: $$K_i + U_i = K_f + U_f$$

Question 13

What is the escape velocity from Earth, given by the formula $$v_{	ext{esc}} = \sqrt{\dfrac{2GM}{R}}$$? What does $$G$$ represent?

Accepted Answer

$$G is $$the universal gravitational constant

Question 14

A car of mass $$1400\ \mathrm{kg}$$ climbs a $$10^\circ$$ hill at $$18\ \mathrm{km/h}. $$What is the power required to overcome gravity?

Accepted Answer

$$P = mgv \sin 	heta$$

Question 15

Which of the following statements about conservative forces is TRUE?

Accepted Answer

The work done by a conservative force is independent of the path taken

Question 16

A block attached to a horizontal spring ($$k = 180\ \mathrm{N/m}) is $$compressed $$5.0\ \mathrm{cm}$$ and released. It stretches $$2.3\ \mathrm{cm}$$ beyond equilibrium before stopping. What is the coefficient of kinetic friction?

Accepted Answer

$$\mu_k = \dfrac{\dfrac{1}{2}k(x_1$^2 - x_2$^2)}{mg(x_1$ + x_2$)}$$

Question 17

Which formula gives the period $$T of an $$object in uniform circular motion in terms of frequency $$f$$?

Accepted Answer

$$T = \dfrac{1}{f}$$

Question 18

A force $$F(y) = (15 	imes 10^2$\ \mathrm{N/m})y - (1.9 	imes 10^3$\ \mathrm{N/m^2$})y^2$ acts over y = 0$ to y = 0.20$$\ \mathrm{m}$$. What is the work done?

Accepted Answer

$$W = \$$int_0$$^{0.20} F(y)\,dy$$

PHYS 215 Test #2 Review: Forces, Newton's Laws, Circular Motion, Energy, and Power

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