Q: A baseball is thrown horizontally from a height of $$2.5\ \mathrm{m}$$ and lands $$20\ \mathrm{m}$$ away. What is the initial speed of the baseball? (Assume $$g = 9.8\ \mathrm{m/s^2$}.)$$

$$20 / \sqrt{2 \times 2.5 / 9.8} \approx 24.8\ \mathrm{m/s}$$

Q: A couch of mass $$85\ \mathrm{kg} is at $$rest on a floor with a coefficient of static friction $$\mu_s = 0.25. $$What is the maximum force that can be applied before the couch starts to move?

$$85 \times 9.8 \times 0.25 = 208.25\ \mathrm{N}$$

Q: A ferris wheel rotates at $$10\ \mathrm{rpm}$$ and completes 1 revolution every 2 minutes. What is the angular speed in $$\mathrm{rad/s}$$?

$$10 \times 2\pi / 60 = 1.05\ \mathrm{rad/s}$$

Q: A student with mass $$40\ \mathrm{kg}$$ stands on the edge of a frictionless disk of radius $$3.0\ \mathrm{m}$$, which spins at $$2.0\ \mathrm{rad/s}. $$What is the centripetal force acting on the student?

$$F_c = m r \$$omega^2$$ = 40 \times 3.0 \times (2.0)^2$ = 480\ \mathrm{N}$$

Q: A ball is tied to a string and whirled in a vertical circle of radius $$1.0\ \mathrm{m}. At $$the top of the circle, what is the minimum speed required for the ball to maintain circular motion?

$$v = \sqrt{g r} = \sqrt{9.8 \times 1.0} = 3.13\ \mathrm{m/s}$$

Question 1

A student stands at rest and then begins walking at a constant velocity. Which of the following best describes the shape of the velocity vs. time graph for this motion?

Accepted Answer

A horizontal line at zero followed by a horizontal line above zero.

Question 2

A ball is tossed straight down from a cliff with a velocity of $$-4\ \mathrm{m/s}$$ from rest. What is the ball's velocity after 2 seconds? (Assume $$g = 9.8\ \mathrm{m/s^2$}$$ downward.)

Accepted Answer

$$-23.6\ \mathrm{m/s}$$

Question 3

Given the position vs. time graph of an object moving in one dimension, how do you determine the object's velocity at a specific time?

Accepted Answer

Find the slope of the tangent to the curve at that time.

Question 4

A baseball is thrown horizontally from a height of $$2.5\ \mathrm{m}$$ and lands $$20\ \mathrm{m}$$ away. What is the initial speed of the baseball? (Assume $$g = 9.8\ \mathrm{m/s^2$}.)$$

Accepted Answer

$$20 / \sqrt{2 	imes 2.5 / 9.8} \approx 24.8\ \mathrm{m/s}$$

Question 5

A box of mass $$m is $$pushed with a horizontal force $$F on a $$rough surface with friction. If the box does not move, what is the magnitude of the friction force?

Accepted Answer

$$F$$

Question 6

A $$2.5\ \mathrm{kg}$$ object is sitting on a surface. What is the normal force acting on the object?

Accepted Answer

$$24.5\ \mathrm{N}$$

Question 7

A couch of mass $$85\ \mathrm{kg} is at $$rest on a floor with a coefficient of static friction $$\mu_s = 0.25. $$What is the maximum force that can be applied before the couch starts to move?

Accepted Answer

$$85 	imes 9.8 	imes 0.25 = 208.25\ \mathrm{N}$$

Question 8

What is the difference between tangential speed and angular speed for an object in uniform circular motion?

Accepted Answer

Tangential speed is $$v = r \omega$$, angular speed is $$\omega = v / r.$$

Question 9

A person sits halfway from the center to the edge of a carousel, then moves to the edge. How does the angular speed compare between both positions?

Accepted Answer

The angular speed is the same at both positions.

Question 10

A ferris wheel rotates at $$10\ \mathrm{rpm}$$ and completes 1 revolution every 2 minutes. What is the angular speed in $$\mathrm{rad/s}$$?

Accepted Answer

$$10 	imes 2\pi / 60 = 1.05\ \mathrm{rad/s}$$

Question 11

A student with mass $$40\ \mathrm{kg}$$ stands on the edge of a frictionless disk of radius $$3.0\ \mathrm{m}$$, which spins at $$2.0\ \mathrm{rad/s}. $$What is the centripetal force acting on the student?

Accepted Answer

$$F_c = m r \$$omega^2$$ = 40 	imes 3.0 	imes (2.0)^2$ = 480\ \mathrm{N}$$

Question 12

A ball is tied to a string and whirled in a vertical circle of radius $$1.0\ \mathrm{m}. At $$the top of the circle, what is the minimum speed required for the ball to maintain circular motion?

Accepted Answer

$$v = \sqrt{g r} = \sqrt{9.8 	imes 1.0} = 3.13\ \mathrm{m/s}$$

Question 13

Two identical rocks are being held by a student at the top of a bridge. The student drops the first rock and throws the second rock horizontally at the same time. Which rock hits the ground first?

Accepted Answer

Both rocks hit the ground at the same time.

Question 14

A box is pushed with a force $$F$$ and accelerates to the right on a rough surface. Which of the following free-body diagrams is correct?

Accepted Answer

Arrows for $$F to $$the right, friction to the left, normal up, gravity down.

Question 15

A car falls off a cliff horizontally. What is the magnitude of its velocity right before it hits the ground if the cliff is $$80\ \mathrm{m}$$ high? (Assume $$g = 9.8\ \mathrm{m/s^2$}$$ and initial horizontal velocity $$v_x = 20\ \mathrm{m/s}.)$$

Accepted Answer

$$v = \sqrt{v_x^2$ + v_y^2$}$$, where $$v_y = \sqrt{2 g h} = \sqrt{2 	imes 9.8 	imes 80} = 39.6\ \mathrm{m/s}$$, so $$v = \sqrt{20^2$ + 39.6^2$} \approx 44.3\ \mathrm{m/s}$$

Physics Semester 1 Exam Review: Study Notes on Kinematics, Forces, and Circular Motion

스터디 가이드 - 연습 문제

학습 가이드 - 플래시카드