Physics Chapter 4

An apple weighs 1 N. When the apple is held at rest above your head, the net force on the apple is

0 N.

A sack of potatoes weighing 200 N falls from an airplane. As the velocity of fall increases, air resistance also increases. When air resistance equals 200 N, the sack's acceleration becomes

0 m/s2.

An apple at rest weighs 1 N. The net force on the apple when it is in free fall is

1 N

The mass of a pet turtle that weighs 10 N is about

1 kg.

The force of friction on a sliding object is 10 N. The applied force needed to maintain a constant velocity is

10 N.

The mass of a lamb that weights 110 N is about

11kg

A tow truck exerts a force of 3000 N on a car, which then accelerates at 2 m/s2. What is the mass of the car?

1500 kg

A jumbo jet has a mass of 100,000 kg. The thrust for each of its four engines is 50,000 N. What is the jet's acceleration when taking off?

2 m/s2

A car traveling at 22 m/s comes to an abrupt halt in 0.1 second when it hits a tree. What is the deceleration of the car?

220 m/s2

Nellie pulls on a 10-kg wagon with a constant horizontal force of 30 N. If there are no other horizontal forces, what is the wagon's acceleration?

3.0 m/s2

A 2000-kg car experiences a braking force of 10,000 N and skids to a stop in 6 seconds. The speed of the car just before the brakes were applied was

30 m/s.

A 500-N parachutist opens his chute and experiences an air resistance force of 800 N. The net force on the parachutist is then

300 N upward.

If you are driving at 20 m/s and slam on your brakes and skid at 0.5g to a full stop, the skidding time is about

4s.

A mobile phone is pulled northward by a force of 10 N and at the same time pulled southward by another force of 15 N. The resultant force on the phone is

5 N.

A 10-kilogram block with an initial velocity of 10 m/s slides 10 meters across a horizontal surface and comes to rest. It takes the block 2 seconds to stop. The stopping force acting on the block is about

50 N

The human body can withstand an acceleration of 10 g under certain conditions. What net force would produce this acceleration for a 50-kg person?

5000 N

A block is dragged without acceleration in a straight-line path across a level surface by a force of 6 N. What is the force of friction between the block and the surface?

6 N

A light woman and a heavy man jump from an airplane at the same time and open their same-size parachutes at the same time. Which person will get to the ground first?

The heavy man

At equilibrium on a bathroom weighting scale, the downward pull of gravity on you is balanced by

an upward support force.

You drive your car at a constant 60 km/h along the highway. You apply the brakes until the car slows to 40 km/h. If at that moment you suddenly release the brakes, the car tends to

continue moving at 40 km/h.

Suzie Skydiver jumps from a high-flying plane. As her velocity of fall increases, her acceleration

decreases.

A large and a small person wish to parachute at equal terminal velocities. The larger person should

get a larger parachute.

A heavy rock and a light rock of the same size are falling through the air from a tall building. The one that encounters the greatest air resistance is the

heavy rock.

When the bottom string is pulled slowly in the heavy-ball-and-strings demonstration (Figure 4.8 in your book), tension

in the top string is due to your pull plus the weight of the ball.

If an object's mass is decreasing while a constant force is applied to the object, the acceleration

increases.

A skydiver steps from a helicopter and falls for a few seconds until terminal velocity is reached. Thereafter, until he opens his parachute, his acceleration

is zero.

Whenever the net force on an object is zero, its acceleration

is zero.

A single brick falls with acceleration g. The reason a double brick falls with the same acceleration is

its ratio of force to mass is the same.

A ball is thrown upwards and caught when it returns. Compared with its initial speed and in the presence of air resistance, the speed with which it is caught is always

less.

A rock is thrown vertically into the air. At the top of its path the net force on it is

mg

A ball is thrown vertically into the air. Because of air resistance, its time coming down compared to its time going up is

more.

Compared to a 1-kg block of solid iron, a 2-kg block of solid iron has the same

none of the above

A car by itself is capable of a certain maximum acceleration. When it tows a car of the same mass, its maximum acceleration is

one half.

Two factors that greatly affect air resistance on falling objects are frontal area and

speed.

Your weight as measured on your bathroom scale is

the force due to gravity on you.

Strange as it may seem, it is just as difficult to accelerate a car on a level surface on the Moon as it is here on Earth because

the mass of the car is independent of gravity.

A feather and a coin will have equal accelerations when falling in a vacuum because

the ratio of both the feather's and coin's weight to mass is the same.

A bowling ball and a baseball accelerate equally when falling in a vacuum because

the ratio of their weights to mass is the same.

A heavy ball hangs by a string, with a second string attached to its bottom. A slow pull on the bottom string breaks the

top string.

A boulder following a straight-line path at constant velocity has

zero acceleration

When a falling object has reached its terminal velocity, its acceleration is

zero.