Question 1

A 40.0 N box rests on a horizontal surface. The coefficient of static friction is 0.40, and the coefficient of kinetic friction is 0.20. What is the minimum horizontal force required to start moving the box?

Accepted Answer

$$16.0\ \mathrm{N}$$

Question 2

A 65 kg person stands on a scale in an elevator accelerating upward at $$2.0\ \mathrm{m/s^2$}. $$What does the scale read?

Accepted Answer

$$767\ \mathrm{N}$$

Question 3

A block is pulled with a force $$T on a $$horizontal surface. The block just starts to move when $$T = \mu_s n. $$What happens to the friction force as the block continues to move at constant velocity?

Accepted Answer

It becomes $$\mu_k n$$, which is less than $$\mu_s n.$$

Question 4

A car of mass $$m$$ rounds a flat curve of radius $$R. If $$the coefficient of static friction is $$\mu_s$$, what is the maximum speed the car can have without sliding?

Accepted Answer

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

Question 5

Two blocks, A and B, are connected by strings and pulled to the right on a frictionless surface. How does the tension in string 1 ($$T_1) $$compare to the tension in string 2 ($$T_2$$)?

Accepted Answer

$$T_1$$ \u003e $$T_2$$

Question 6

A block is pressed against the vertical side of a cart. The coefficient of static friction is $$\mu_s. $$What is the minimum acceleration $$a of $$the cart so the block does not fall?

Accepted Answer

$$a = \frac{g}{\mu_s}$$

Question 7

A satellite of mass $$m$$ orbits Earth at a distance $$r$$ from the center. What is the gravitational force acting on the satellite?

Accepted Answer

$$F_g = \frac{G M_{E} m}{r^2$}$$

Question 8

A Ferris wheel rotates at a constant speed. At the highest point, the upward force from the seat is one-fourth of Jack's weight. What is the radius $$R of $$the Ferris wheel if the speed is $$v$$?

Accepted Answer

$$R = \frac{4v^2$}{3g}$$

Question 9

A sled moves in a circle on frictionless ice, attached to a post by a rope. If the rope breaks, what path does the sled follow?

Accepted Answer

It moves in a straight line tangent to the circle.

Question 10

Which of the following statements about Newton’s Third Law is correct?

Accepted Answer

Forces between two objects are equal in magnitude and opposite in direction, but act on different objects.

Question 11

A satellite orbits Earth at radius $$r. $$What is the period $$T of $$its orbit?

Accepted Answer

$$T = 2\pi \sqrt{\frac{r^3$}{G M_E}}$$

Question 12

A block is moving to the left at constant velocity. What can you conclude about the net force on the block?

Accepted Answer

The net force is zero.

Question 13

A block of mass $$m is $$acted upon by two forces: $$3\ \mathrm{N} to $$the left and $$4\ \mathrm{N} to $$the right. What can you say about the block’s motion?

Accepted Answer

It could be moving in either direction or be instantaneously at rest.

Question 14

A box is at rest on a horizontal surface. What is the magnitude of the friction force acting on it?

Accepted Answer

Zero

Question 15

If the net force on an object is zero, which of the following must be true?

Accepted Answer

The object remains at rest or moves with constant velocity.

Question 16

A block slides down an incline at constant speed. What is the direction of the friction force on the block?

Accepted Answer

Up the incline, opposing the motion.

Question 17

A satellite in orbit has a mass $$m$$ and is at height $$h$$ above Earth's surface. Which of the following is true about its speed?

Accepted Answer

It is independent of the satellite's mass.

Question 18

A block is placed on a ramp and moves at constant speed. The coefficient of kinetic friction is $$\mu_k. $$What is the friction force acting on the block?

Accepted Answer

$$f_k = \mu_k n$$

Question 19

If the gravitational force between two objects is $$F$$ when they are separated by distance $$r$$, what will the force be if the distance is doubled?

Accepted Answer

$$F/4$$

Newton’s Laws, Forces, Friction, Circular Motion, and Gravitation – Study Notes

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