Q: The maximum force of static friction between two surfaces is given by:

$$F_{s,\text{max}} = \mu_s F_n$$

Q: A ball is thrown at an angle $$\theta to $$the horizontal with speed $$v. $$What are the $$x$$ and $$y$$ components of its velocity?

$$v_x = v \cos \theta$$, $$v_y = v \sin \theta$$

Q: A hiker pulls a friend up a hill at $$30^\circ$$ with a cable. If the coefficient of static friction is $$0.80$$ and the hiker's mass is $$65 kg$$, what is the maximum force the hiker can exert without slipping?

$$F_{\text{max}} = mg(\mu_s \cos 30^\circ - \sin 30^\circ)$$

Question 1

A ball is dropped from a moving cart. In the Earth reference frame, what is the trajectory of the ball?

Accepted Answer

A parabolic curve

Question 2

Which of the following statements about vector addition and subtraction is correct?

Accepted Answer

Vector addition is commutative, but vector subtraction is not

Question 3

A vector $$f{A}$$ has components $$A_x = 3$$ and $$A_y = 4. $$What is the magnitude of $$f{A}$$?

Accepted Answer

$$A = 5$$

Question 4

A brick slides down an incline with negligible friction. Which component of the gravitational force causes the brick to accelerate?

Accepted Answer

The component parallel to the incline

Question 5

The maximum force of static friction between two surfaces is given by:

Accepted Answer

$$F_{s,	ext{max}} = \mu_s F_n$$

Question 6

A crate is at rest on the floor. As you push harder, but it does not move, what happens to the force of static friction?

Accepted Answer

It increases in magnitude

Question 7

Which of the following best describes the work done by gravity when an object descends a vertical distance $$h$$?

Accepted Answer

$$W = mgh$$

Question 8

A ball is thrown at an angle $$	heta to $$the horizontal with speed $$v. $$What are the $$x$$ and $$y$$ components of its velocity?

Accepted Answer

$$v_x = v \cos 	heta$$, $$v_y = v \sin 	heta$$

Question 9

At the highest point of a projectile's trajectory, what is true about its velocity and acceleration?

Accepted Answer

Vertical velocity is zero, but acceleration is $$g$$ downward

Question 10

A baseball is hit with initial velocity components $$u_{x,i} = 30 m/s $$and $$u_{y,i} = 40 m/s. $$What is the speed at the highest point?

Accepted Answer

30 m/s

Question 11

The scalar (dot) product of two vectors $$\bf{A}$$ and $$\bf{B} is $$zero when:

Accepted Answer

The vectors are perpendicular

Question 12

A hiker pulls a friend up a hill at $$30^\circ$$ with a cable. If the coefficient of static friction is $$0.80$$ and the hiker's mass is $$65 kg$$, what is the maximum force the hiker can exert without slipping?

Accepted Answer

$$F_{	ext{max}} = mg(\mu_s \cos 30^\circ - \sin 30^\circ)$$

Question 13

In two-dimensional collisions, conservation of momentum requires:

Accepted Answer

Both x and y components of momentum are conserved

Question 14

For a block sliding down an incline, the work done by gravity is independent of:

Accepted Answer

The path taken

Question 15

The coefficient of kinetic friction $$\mu_k is $$always:

Accepted Answer

Less than or equal to the coefficient of static friction $$\mu_s$$

Question 16

A suitcase on a conveyor belt inclined at $$20^\circ$$ accelerates at $$4.0 m/s$^2$$ before slipping. What is the coefficient of static friction?

Accepted Answer

$$\mu_s = \frac{a + g \sin 20^\circ}{g \cos 20^\circ}$$

Question 17

Which of the following is true about the force of kinetic friction?

Accepted Answer

It is independent of contact area and speed

Question 18

The work done by a constant force $$\bf{F}$$ over displacement $$\Delta \bf{r} is$$:

Accepted Answer

$$W = \bf{F} \cdot \Delta \bf{r}$$

Question 19

If a block slides down an incline and the normal force is perpendicular to the displacement, what is the work done by the normal force?

Accepted Answer

Zero

Motion in a Plane: Vectors, Forces, Friction, and Work

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