Q: A projectile is launched from the ground with an initial speed $$v_0 at an $$angle $$\theta$$ above the horizontal, as shown in the image. What is the time of flight until the projectile lands back on the ground? (Neglect air resistance.)

$$\frac{2 v_0$ \sin \theta}{g}$$

Q: A block of mass $$m is at $$rest on a rough inclined plane at angle $$\theta. $$The coefficient of static friction is $$\mu_s. $$What is the maximum angle $$\theta_{max}$$ before the block starts to slide?

$$\theta_{max} = \arctan(\mu_s)$$

Question 1

A projectile is launched from the ground with an initial speed $$v_0 at an $$angle $$	heta$$ above the horizontal, as shown in the image. What is the time of flight until the projectile lands back on the ground? (Neglect air resistance.)

Accepted Answer

$$\frac{2 v_0$ \sin 	heta}{g}$$

Question 2

A person stands in an elevator that is moving upward at constant speed. The upward normal force $$N$$ exerted by the elevator floor on the person is:

Accepted Answer

$$N = W$$

Question 3

If the elevator in the previous question begins to accelerate upward, how does the normal force $$N$$ compare to the weight $$W of $$the person?

Accepted Answer

$$N \u003e W$$

Question 4

A block of mass $$m is $$pulled along a rough table at constant velocity with an external force $$F at $$some angle above the horizontal. Which equation correctly represents the $$y-$$component (vertical) force balance?

Accepted Answer

$$N + F \sin 	heta = mg$$

Question 5

A mass $$m is $$pulled along a rough table at constant velocity with an external force $$F at $$some angle above the horizontal. Which equation correctly represents the $$x-$$component (horizontal) force balance?

Accepted Answer

$$F \cos 	heta = f_k$$

Question 6

A block of mass $$m$$ sits on a frictionless inclined plane at angle $$	heta. $$What is the component of the gravitational force parallel to the incline?

Accepted Answer

$$mg \sin 	heta$$

Question 7

A block of mass $$m$$ sits on a frictionless inclined plane at angle $$	heta. $$What is the component of the gravitational force perpendicular to the incline?

Accepted Answer

$$mg \cos 	heta$$

Question 8

Two blocks, A and B, are in contact on a frictionless air track as shown. If you push on block A, which statement is true about the force that block B exerts on block A?

Accepted Answer

It is equal in magnitude and opposite in direction to the force A exerts on B.

Question 9

A mass $$m is $$attached to a string and swung in a horizontal circle at constant speed $$v ($$conical pendulum). What is the direction of the net force on the mass?

Accepted Answer

Toward the center of the circle

Question 10

A motorcycle is turning in a circle of radius $$r on a $$flat road. If the coefficient of static friction is $$\mu_s$$, what is the maximum speed $$v_{max}$$ before the motorcycle starts to slide?

Accepted Answer

$$v_{max} = \sqrt{\mu_s g r}$$

Question 11

A child pulls a sled of mass $$m$$ with a force $$F at an $$angle $$	heta$$ above the horizontal. If the sled moves at constant velocity, what is the correct expression for the normal force $$N$$?

Accepted Answer

$$N = mg - F \sin 	heta$$

Question 12

A block of mass $$m is at $$rest on a rough inclined plane at angle $$	heta. $$The coefficient of static friction is $$\mu_s. $$What is the maximum angle $$	heta_{max}$$ before the block starts to slide?

Accepted Answer

$$	heta_{max} = \arctan(\mu_s)$$

Question 13

A mass $$m is $$attached to a string and swung in a horizontal circle of radius $$R at $$speed $$v. $$What is the tension $$T in $$the string (neglect gravity)?

Accepted Answer

$$T = \frac{mv^2$}{R}$$

Question 14

A book sits at rest on a table. Which of the following statements is correct?

Accepted Answer

The normal force from the table equals the weight of the book.

Question 15

A book sits at rest on a table. Are the normal force and the weight force members of a Newton's Third Law action-reaction pair?

Accepted Answer

No, they act on the same object.

Question 16

A person pushes a heavy box across a rough floor and the box accelerates. Which statement is correct?

Accepted Answer

The force you exert on the box is equal in magnitude to the force the box exerts on you.

Question 17

A block slides down a frictionless ramp. If the block is moving uphill (after being pushed up), what is the direction of the net force?

Accepted Answer

Down the ramp, same as before.

Question 18

A velocity vs. time graph for an object is shown as a straight line with positive slope. What does this indicate about the object's acceleration?

Accepted Answer

The acceleration is constant and positive.

Question 19

A crate is hanging from the ceiling by two angled cables. The left cable makes a $$40^\circ$$ angle with the horizontal, and the right cable makes a $$30^\circ$$ angle. The crate has mass $$5\,\mathrm{kg}. $$Which equation must be satisfied for vertical force equilibrium?

Accepted Answer

$$T_1$$ \sin 40^\circ + $$T_2$$ \sin 30^\circ = mg$$

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