Q: A 38.4 kg crate is pushed on a horizontal floor. The crate begins to move when the applied force exceeds 320 N. What is the coefficient of static friction between the crate and the floor?

$$\mu_s = \frac{320}{38.4 \times 9.8} = 0.851$$

Q: A car travels around a banked curve of radius $$R at $$speed $$v. If $$the curve is banked at an angle $$\beta so $$that no friction is required, which equation gives the correct banking angle?

$$\tan(\beta) = \frac{v^2$}{gR}$$

Q: A 58 kg student stands on a scale in a lift. The lift starts moving up with acceleration $$a_g = -1.9 m/s$^2. $$What is the reading on the scale?

$$T = 58 \times (9.8 + 1.9) = 671 N$$

Q: A wrenching ball of mass $$m is $$held by a cable at angle $$\theta to $$the vertical. What is the tension in the cable?

$$T = \frac{mg}{\cos(\theta)}$$

Question 1

Which of the following best describes Newton's First Law of Motion?

Accepted Answer

An object will remain at rest or move with constant velocity unless acted upon by a net external force.

Question 2

A block of ice of mass $$m is $$pushed across a frictionless surface with a constant force $$F. $$What is the acceleration of the block?

Accepted Answer

$$a = \frac{F}{m}$$

Question 3

A 38.4 kg crate is pushed on a horizontal floor. The crate begins to move when the applied force exceeds 320 N. What is the coefficient of static friction between the crate and the floor?

Accepted Answer

$$\mu_s = \frac{320}{38.4 	imes 9.8} = 0.851$$

Question 4

Which equation correctly expresses Newton's Second Law in vector form?

Accepted Answer

$$\sum \vec{F} = m \vec{a}$$

Question 5

A car travels around a banked curve of radius $$R at $$speed $$v. If $$the curve is banked at an angle $$\beta so $$that no friction is required, which equation gives the correct banking angle?

Accepted Answer

$$	an(\beta) = \frac{v^2$}{gR}$$

Question 6

A ball falls through air and eventually reaches terminal speed $$v_t. $$Which equation gives the terminal speed if the drag force is $$F_{drag} = kv$$?

Accepted Answer

$$v_t = \frac{mg}{k}$$

Question 7

A block is pulled by three forces: $$F_1 = 985$ N at 31$$^\circ$$, F_2$ = 788 N at$$ $$122^\circ$$, and $$F_3 = 411$ N at 233$$^\circ$$. What is the magnitude of the resultant force?

Accepted Answer

$$R = \sqrt{179^2$ + 847^2$} = 866 N$$

Question 8

Which statement about friction is correct?

Accepted Answer

The coefficient of kinetic friction is usually smaller than the coefficient of static friction.

Question 9

A 58 kg student stands on a scale in a lift. The lift starts moving up with acceleration $$a_g = -1.9 m/s$^2. $$What is the reading on the scale?

Accepted Answer

$$T = 58 	imes (9.8 + 1.9) = 671 N$$

Question 10

Which of the following is an example of a long-range force?

Accepted Answer

Gravitational force

Question 11

A block of mass $$m is on an $$inclined plane at angle $$\alpha. $$What is the normal force acting on the block?

Accepted Answer

$$N = mg \cos(\alpha)$$

Question 12

A conical pendulum of length $$L$$ swings with bob mass $$m at $$angle $$\beta. $$What is the period of rotation?

Accepted Answer

$$T = 2\pi \sqrt{\frac{L \cos(\beta)}{g}}$$

Question 13

A passenger in a car moving in a circle of radius $$R at $$constant speed $$v$$ experiences a force at the top of the circle. What is the expression for the normal force at the top?

Accepted Answer

$$N_T = mg \left[1 - \frac{v^2$}{gR}\right]$$

Question 14

Which of the following is the correct expression for the maximum static friction force?

Accepted Answer

$$f_{s, max} = \mu_s N$$

Question 15

A wrenching ball of mass $$m is $$held by a cable at angle $$	heta to $$the vertical. What is the tension in the cable?

Accepted Answer

$$T = \frac{mg}{\cos(	heta)}$$

Question 16

A block of mass $$m is $$sliding on a surface with kinetic friction coefficient $$\mu_k. $$What is the frictional force acting on the block?

Accepted Answer

$$f_k = \mu_k N$$

Question 17

Which of the following is NOT a contact force?

Accepted Answer

Gravitational force

Question 18

A ball of mass $$m is $$dropped and experiences air resistance proportional to its speed. Which equation describes its motion before reaching terminal speed?

Accepted Answer

$$m \frac{dv}{dt} = mg - kv$$

Question 19

A car of mass $$m$$ moves in a circle of radius $$R at $$constant speed $$v. $$What is the magnitude of the net force required to keep it moving in a circle?

Accepted Answer

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

DR1- Newton's Laws of Motion

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