Ch3-Ch4

Consulting the graph shown in (Figure 1), determine the object's average velocity over the time interval from 2 to 4 seconds.

5 m/s

Three cars drive around a perfectly circular track. The speedometers in the figure below show the speed of each car over the same 10-s time interval. Which of the cars are accelerating?

Cars A, B, and C

Why does the distance traveled by the ball in each half second after it is released change in the way in which it does?

Gravity is pulling down on the ball, so it accelerates down at a steady rate.

After he gets the block to move, what does Dr. Hewitt do to drag the block across the table at a steady rate?

He continues to apply a steady force.

Consider the video demonstration that you just watched. Which of the following changes could potentially allow the ball on the straight inclined (yellow) track to win? Ignore air resistance.

Increase the tilt of the yellow track.

Suppose a runner completes one lap around a 400-m track in a time of 50 s. Calculate the magnitude of the average velocity of the runner.

0 m/s

An object covers a distance of 8 meters in the first second of travel, another 8 meters during the next second, and 8 meters again during the third second. Its acceleration is

0 m/s2.

Suppose a runner completes one lap around a 400-m track in a time of 50 s. Calculate the average speed of the runner.

400m /50s =8 m/s

A 300-kg bear grasping a vertical tree slides down at constant velocity. The friction force between the tree and the bear is

= 30-kg x 10= 3000 N

What is the net force acting on a falling 1-kg ball if it encounters 2 N of air resistance? Express your answer with the appropriate units.

A 1 kg ball has a weight of (1 kg * 10 m/s which is equal to 10 N. Air resistance is a force in the opposite direction to a falling weight so the net force acting on the ball is 10 N - 2 N =8.00 N

Which of the motion diagrams in the figure below best matches the motion of the bungee jumper shown in the video?

C

If Dr. Hewitt applies 3 N of force to keep the block moving at a steady rate, what must be the force of friction, and why?

Equal to 3 N, because the force of friction should exactly balance out the force Dr. Hewitt applies, so that there is no net force acting on the block.

You are dragging a block on a surface with friction at a steady speed of 2 m/s and exert a force of 5 N to do so. What is the force of friction? Why?

Equal to 5 N, because the force of friction should exactly balance out the force Dr. Hewitt applies, so that there is no net force acting on the block.

Use the "Force applied" slider to set the force applied on the elephant to somewhere in the middle of the range. After you have set the "Force applied" slider, do not change it again for this question. How would the acceleration change if the mass of the elephant were increased?

It decreases.

What is the distance fallen for a freely falling object 1 s after being dropped from a rest position? What is the distance for a 4-s drop?

It falls 5 m in 1 s and 80 m in 4 s. Rounding g=10 d = 1/2gt^2, After 1 second 5m, after 4 s 80m

How does the distance traveled by the ball in the second half second compare with the distance traveled by the ball in the first half second?

It increases.

Use the "Mass of elephant" slider to set the mass of the elephant to somewhere in the middle of the range. After you have set the "Mass of elephant" slider, do not change it again for this question. How would the acceleration change if the applied force on the elephant were increased?

It increases.

What is the acceleration of the ball when it is moving up, when it is at the maximum height, and when it is moving down? (Note: The acceleration graph is shown in red.)

It is always negative.

What is the value of the velocity of the ball when it reaches its maximum height?

It is always zero.

Four cars undergo acceleration as described by the data in the following table. Initial V Final V Time period A 2.0 11.0 3.0 B -5.0 3.0 2.0 C 1.0 -5.0 2.0 D 0.0 25.0 10.0 *Remember that the starting time is 0 sec*

The average accelerations, from most positive to most negative, are as follows: (B) 4 m/s2, (A) 3 m/s2, (D) 2.5 m/s2, and (C) −3 m/s2. 11.0 -2.0 / 3.0 - 0 = 3 25.0 / 10.0 = 2.5

What general rule can you conclude about the force needed to keep an object in motion at a steady rate?

The force that you need to apply to keep an object moving at a steady rate is equal to the force resisting the motion of the object.

What is the average speed in kilometers per hour of a horse that gallops a distance of 15 km in a time of 30 min?

The horses speed is 30 km/h (formula is d = 15 speed/time (0.5) = 30 km/h

Suppose you are hiking along a trail. Make a comparison between the magnitude of your displacement and your distance traveled.

The magnitude of your displacement can be equal to your distance traveled. The magnitude of your displacement can be less than your distance traveled.

An object cannot remain at rest unless which of the following holds?

The net force acting on it is zero.

If a block is moving to the left at a constant velocity, what can one conclude?

The net force applied to the block is zero.

Surprisingly, very few athletes can jump more than 2 feet (0.6 m) straight up. Use d=1/2gt2 and solve for the time one spends moving upward in a 0.6-m vertical jump. Then double it for the "hang time"-the time one's feet are off the ground.

a) t= sqrt of 2 * 0.6 / 10 m/s^2 Hangtime=0.35 s x 2= 0.70

How can you use the graph of velocity versus time to estimate the acceleration of the ball?

by estimating the value of the slope of the graph

Two forces, of magnitude 4N and 10N, are applied to an object. The relative direction of the forces is unknown. The net force acting on the object _

cannot have a magnitude equal to 5N

A vehicle undergoes acceleration when it

changes its direction. loses speed. gains speed. all of the above

Which of the following best describes the acceleration of a bungee jumper during free fall?

constant

A ball starting from rest at the top of an inclined plane accelerates at 2 m/s2 and reaches the bottom of the plane in 3 seconds. What is the length of the plane? 3^2?

d = 1/2 a * t = d= t^2 =9 m

A block of mass 2kg is acted upon by two forces: 3N (directed to the left) and 4N (directed to the right). What can you say about the block's motion?

it could be moving to the left, moving to the right, or be instantaneously at rest.

A massive block is being pulled along a horizontal frictionless surface by a constant horizontal force. The block must be

moving with a constant nonzero acceleration

a cart maintains a constant velocity of 100 m/s for 10 seconds. During this interval its acceleration is

zero.