Question 1

An astronaut in orbit around Earth experiences 'weightlessness.' Which of the following best explains this phenomenon?

Accepted Answer

The astronaut is in free-fall, so the only force acting is gravity, resulting in zero apparent weight.

Question 2

A patient’s leg is suspended by a system of ropes and pulleys in a hospital. If the pulleys and ropes are massless and frictionless, what is true about the tension in the rope segments supporting the leg?

Accepted Answer

The tension is the same throughout all segments of the rope.

Question 3

A box of mass $$m is at $$rest on a horizontal surface. Which equation correctly represents the condition for equilibrium in the vertical direction?

Accepted Answer

$$\sum F_y = 0$$

Question 4

A person stands on a scale in an elevator that is accelerating upward with acceleration $$a. If $$the person’s mass is $$m$$, what does the scale read?

Accepted Answer

$$m(g+a)$$

Question 5

Two blocks, $$m_1$$ and $$m_2$$, are in contact on a frictionless table. A force $$F is $$applied to $$m_1. $$What is the acceleration of the system?

Accepted Answer

$$a = \frac{F}{m_1$ + m_2$}$$

Question 6

A block is pulled by a rope with tension $$T$$ across a frictionless surface. According to Newton’s third law, what is the reaction force to the tension $$T$$?

Accepted Answer

The force the block exerts on the rope.

Question 7

A 70 kg astronaut is floating inside the International Space Station. What is the astronaut’s weight and apparent weight?

Accepted Answer

Weight is $$686 N$$, apparent weight is $$0 N.$$

Question 8

A person in an elevator feels lighter than normal. Which of the following best describes the motion of the elevator?

Accepted Answer

The elevator is accelerating downward.

Question 9

A block of mass $$m is $$suspended by a rope over a massless, frictionless pulley. What is the tension in the rope if the block is at rest?

Accepted Answer

$$T = mg$$

Question 10

A 10 kg box is pulled across a horizontal surface with a force of 50 N. If the coefficient of kinetic friction is $$\mu_k = 0.2$$, what is the acceleration of the box? (Take $$g = 9.8 m/s$^2)$$

Accepted Answer

$$a = 3.04 m/s$^2$$

Question 11

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

Accepted Answer

Newton’s second law states that $$\sum \vec{F} = m \vec{a}.$$

Question 12

A block is at rest on a table. Which forces act on the block?

Accepted Answer

Both the gravitational force and the normal force.

Question 13

A 5 kg object is in an elevator descending and slowing down with an acceleration of $$2 m/s$^2. $$What is the normal force acting on the object? ($$g = 9.8 m/s$^2)$$

Accepted Answer

$$59 N$$

Question 14

Two blocks, $$m_1 = 2$ kg and m_2$ = 3 kg$$, are in contact on a frictionless table. A force of $$10 N is $$applied to $$m_1. $$What is the force that $$m_2$$ exerts on $$m_1$$?

Accepted Answer

$$6 N$$

Question 15

A block is pulled upward by a rope at constant velocity. Which statement is true?

Accepted Answer

The tension in the rope equals the weight of the block.

Question 16

A person pushes a box across a rough floor at constant speed. Which of the following is true about the forces acting on the box?

Accepted Answer

The applied force equals the friction force.

Question 17

A block is suspended by two ropes at angles $$\$$theta_1$$ and $$\$$theta_2 to $$the horizontal. Which equation must be satisfied for equilibrium in the vertical direction?

Accepted Answer

$$T_1$$ \sin \$$theta_1$$ + $$T_2$$ \sin \$$theta_2 = mg$

Question 18

A block is pulled by a rope over a pulley. If the rope and pulley are massless and frictionless, what is the acceleration of the block if the only forces are tension $$T$$ and weight $$mg$$?

Accepted Answer

$$a = \frac{T - mg}{m}$$

Question 19

A 20 kg box is lifted using a pulley system with three vertical rope segments supporting the load. What is the force required to lift the box at constant velocity? ($$g = 9.8 m/s$^2)$$

Accepted Answer

$$65.3 N$$

Newton’s Laws, Equilibrium, and Friction: Study Notes

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