Question 1

A 5 kg box is pushed with a constant force of 20 N across a frictionless surface. What is the acceleration of the box?

Accepted Answer

$$a = \frac{20}{5} = 4\ \mathrm{m/s^2$}$$

Question 2

A car of mass 1000 kg accelerates at $$2\ \mathrm{m/s^2$}. $$What is the net force acting on the car?

Accepted Answer

$$F_{\mathrm{net}} = 2000\ \mathrm{N}$$

Question 3

If a constant force causes an object to accelerate at $$4\ \mathrm{m/s^2$}$$, what is the acceleration of an object with twice the mass experiencing the same force?

Accepted Answer

$$2\ \mathrm{m/s^2$}$$

Question 4

An object, when pushed with a net force $$F$$, has an acceleration of $$2\ \mathrm{m/s^2$}. $$Now twice the force is applied to an object that has four times the mass. Its acceleration will be:

Accepted Answer

$$1\ \mathrm{m/s^2$}$$

Question 5

A basketball is released from rest in a stiff breeze directed to the right. What is the direction of the ball's acceleration?

Accepted Answer

Down and to the right, in the direction of the net force

Question 6

A skier speeds up as she skis downhill, while a train travels at constant speed on a straight track. On which is the net force greater?

Accepted Answer

The skier

Question 7

An object on a rope is lowered at constant speed. Which statement is true?

Accepted Answer

The rope tension equals the object's weight

Question 8

An object on a rope is lowered at a steadily decreasing speed. Which statement is true?

Accepted Answer

The rope tension is greater than the object's weight

Question 9

A Boeing 737 (mass $$51,000\ \mathrm{kg}) $$accelerates from rest to $$70\ \mathrm{m/s}$$ over a distance of $$2940\ \mathrm{m}. $$What is the thrust produced by each engine if there are two engines and the acceleration is constant?

Accepted Answer

$$67,000\ \mathrm{N}$$

Question 10

Which of the following is the correct SI unit for force?

Accepted Answer

Newton ($$\mathrm{N})$$

Question 11

A block is pushed across a table at a steady speed. If you are exerting a force on it, why isn't it accelerating?

Accepted Answer

The pushing force is balanced by the friction force, so net force is zero

Question 12

Which equation correctly expresses Newton’s Second Law for a system with multiple forces?

Accepted Answer

$$\vec{F}_{\mathrm{net}} = m\vec{a}$$

Question 13

A free-body diagram for a ball tossed straight up (ignoring air resistance) just after it leaves the hand should show:

Accepted Answer

Only the downward force of gravity

Question 14

A car is parked on a hill. Which force is NOT present in its free-body diagram?

Accepted Answer

Thrust

Question 15

A skier is towed up a snow-covered hill at constant speed. What does the free-body diagram show about the forces acting on the skier?

Accepted Answer

The sum of all forces is zero; forces are balanced

Question 16

If the net force on an object is zero, what can be said about its acceleration?

Accepted Answer

The acceleration is zero

Question 17

A 10 kg object is acted upon by two forces: $$\vec{F}_1 = 30\ \mathrm{N} to $$the right and $$\vec{F}_2 = 10\ \mathrm{N} to $$the left. What is the acceleration of the object?

Accepted Answer

$$a = \frac{30 - 10}{10} = 2\ \mathrm{m/s^2$}$$\ to\ the\ right$

Question 18

A block of mass $$m is $$pulled to the right at constant speed by a force $$F. $$What can be said about the friction force acting on the block?

Accepted Answer

The friction force is equal in magnitude and opposite in direction to $$F$$

Question 19

A 2 kg object is acted upon by a net force of 10 N. What is its acceleration?

Accepted Answer

$$a = \frac{10}{2} = 5\ \mathrm{m/s^2$}$$

L8-10:Newton’s Second Law and Applications: Forces and Free-Body Diagrams

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