If only a single nonzero force acts on an object, must the object have an acceleration relative to any inertial reference frame? Can it ever have zero velocity?

A $4.0-\mathrm{kg}$ object is subjected to two constant forces, $\vec{F}_1=(2.0 \mathrm{~N}) \hat{i}+(-3.0 \mathrm{~N}) \hat{j}$ and $\vec{F}_2=(4.0 \mathrm{~N}) \hat{i}-(11 \mathrm{~N}) \hat{j}$. The object is at rest at the origin at time $t=0$.

$(b)$ What is its velocity at time $t=3.0 \mathrm{~s}$ ?

One busy air route across the Atlantic Ocean is about 5500 km. The now-retired Concord, a supersonic jet capable of flying at twice the speed of sound, was used for traveling such routes.

$(b)$ Compare this time to the time taken by a subsonic jet flying at 0.90 times the speed of sound.

An electron in a television tube travels the $16-\mathrm{cm}$ distance from the grid to the screen at an average speed of $4.0 \times 10^7 \mathrm{~m} / \mathrm{s}$. How long does the trip take?

What is the approximate average velocity of the race cars during the Indianapolis 500 ?

A $4.0-\mathrm{kg}$ object is subjected to two constant forces, $\vec{F}_1=(2.0 \mathrm{~N}) \hat{i}+(-3.0 \mathrm{~N}) \hat{j}$ and $\vec{F}_2=(4.0 \mathrm{~N}) \hat{i}-(11 \mathrm{~N}) \hat{j}$. The object is at rest at the origin at time $t=0$.

$(a)$ What is the object's acceleration?

To drag a 75-kg log along the ground at constant velocity, you have to pull on it with a horizontal force of $250 \mathrm{~N}$. (a) What is the resistive force exerted by the ground? (b) What horizontal force must you exert if you want to give the log an acceleration of $2 \mathrm{~m} / \mathrm{s}^2$ ?

If you push a block whose mass is $m_1$ across a frictionless floor with a horizontal force of a magnitude $F_0$, the block has an acceleration of $12 \mathrm{~m} / \mathrm{s}^2$. If you push on a different block whose mass is $m_2$ with a horizontal force of magnitude $F_0$, its acceleration is $3.0 \mathrm{~m} / \mathrm{s}^2$.

$(b)$ What acceleration will a horizontal force of magnitude $F_0$ give to a single block with mass $m_2+m_1$ ?

If you push a block whose mass is $m_1$ across a frictionless floor with a horizontal force of a magnitude $F_0$, the block has an acceleration of $12 \mathrm{~m} / \mathrm{s}^2$. If you push on a different block whose mass is $m_2$ with a horizontal force of magnitude $F_0$, its acceleration is $3.0 \mathrm{~m} / \mathrm{s}^2$.

$(a)$ What acceleration will a horizontal force of magnitude $F_0$ give to a single block with mass $m_2-m_1$ ?

Al and Bert stand in the middle of a large frozen lake (frictionless surface). $\mathrm{Al}$ pushes on Bert with a force of $20 \mathrm{~N}$ for $1.5 \mathrm{~s}$. Bert's mass is $100 \mathrm{~kg}$. Assume that both are at rest before $\mathrm{Al}$ pushes Bert.

$(b)$ What speed does $\mathrm{Al}$ reach if his mass is $80 \mathrm{~kg}$ ?

Al and Bert stand in the middle of a large frozen lake (frictionless surface). $\mathrm{Al}$ pushes on Bert with a force of $20 \mathrm{~N}$ for $1.5 \mathrm{~s}$. Bert's mass is $100 \mathrm{~kg}$. Assume that both are at rest before $\mathrm{Al}$ pushes Bert.

$(a)$ What is the speed that Bert reaches as he is pushed away from $\mathrm{Al}$ ?

A single force of $12 \mathrm{~N}$ acts on a particle of mass $\mathrm{m}$. The particle starts from rest and travels in a straight line a distance of $18 \mathrm{~m}$ in $6 \mathrm{~s}$. Find $m$.

A force $\vec{F}=(6 \mathrm{~N}) \hat{i}-(3 \mathrm{~N}) \hat{j}$ acts on an object of mass $1.5 \mathrm{~kg}$. Find the acceleration $\vec{a}$. What is the magnitude $a$ ?

A horizontal force of magnitude $F_0$ causes an acceleration of magnitude $3.0 \mathrm{~m} / \mathrm{s}^2$ when it acts on an object of mass $m$ sliding on a frictionless surface. Find the magnitude of the acceleration of the same object in the circumstances shown in Figure 4-35a and $4-35 b$.