midterm

Question 1

When a ball is thrown straight up with no air resistance, the acceleration at its highest point

Answer 1

…is downward

Question 2

Suppose that a car traveling to the west (-x direction) begins to slow down as it approaches a traffic light. Which statement concerning its acceleration must be correct?

Answer 2

its acceleration is positive

Question 3

Two displacement vectors have magnitudes of 5.0 m and 7.0 m, respectively. If these two vectors are added together, the magnitude of the sum

Answer 3

could be as small as 2.0 m or as large as 12 m

Question 4

The eastward component of vector is equal to the westward component of vector and their northward components are equal. Which one of the following statements must be correct for these two vectors?

Answer 4

The magnitude of vector must be equal to the magnitude of vector .

Question 5

A horse pulls a cart with force . As a result of this force the cart accelerates with constant acceleration. The magnitude of the force that the cart exerts on the horse

Answer 5

equal to the magnitude of .

Question 6

Two objects have masses m and 5m, respectively. They both are placed side by side on a frictionless inclined ramp and allowed to slide down from rest without any air resistance. Which one of the following statements about these objects is correct?

Answer 6

The two objects reach the bottom of the ramp at exactly the same time.

Question 7

A push of magnitude P acts on a box of weight W as shown in the figure. The push is directed at an angle θ below the horizontal, and the box remains a rest. The box rests on a horizontal surface that has some friction with the box. The normal force on the box due to the floor is equal to

Answer 7

Correct W + P sin θ.

Question 8

A train travels at a constant speed of 60.4 mi/h for 101.5 min. What distance does the train cover expressed to the correct number of significant figures?

Answer 8

102 mi

Question 9

A ball is projected upward at time t = 0 s, from a point on a flat roof 10 m above the ground. The ball rises and then falls with insignificant air resistance, missing the roof, and strikes the ground. The initial velocity of the ball is Consider all quantities as positive in the upward direction. At time the vertical velocity of the ball is closest to

Answer 9

0 m/s.

Question 10

To determine the height of a bridge above the water, a person drops a stone and measures the time it takes for it to hit the water. If the time is 2.3 s, what is the height of the bridge? Neglect air resistance.

Answer 10

26 m

Question 11

A swimmer heading directly across a river that is 200 m wide reaches the opposite bank in 6 min 40 s. During this swim, she is swept downstream 480 m. What is the speed of the current?

Answer 11

1.2 m/s

Question 12

A player throws a football 50.0 m at 61.0° north of west. What is the westward component of the displacement of the football?

Answer 12

24.2 m

Question 13

The figure shows an acceleration-versus-force graph for three objects pulled by wires. If the mass of object 2 is 36 kg, what are the masses of objects 1 and 3?

Answer 13

12 kg and 90 kg

Question 14

A 50-kg box is resting on a horizontal floor. A force of 250 N directed at an angle of 30.0° below the horizontal is applied to the box. The coefficient of static friction between the box and the surface is 0.40, and the coefficient of kinetic friction is 0.30. What is the force of friction on the box?

Answer 14

220 N

Question 15

A 6.00-kg ornament is held at rest by two light wires that form 30° angles with the vertical, as shown in the figure. An external force of magnitude F acts vertically downward on the ornament. The tension exerted by each of the two wires is denoted by T. A free-body diagram, showing the four forces that act on the box, is shown in the figure. If the magnitude of force F is 410 N, what is the magnitude of the tension T?

Answer 15

271 N

Question 16

A bead is moving with a speed of 20 m/s at position A on the track shown in the figure. This track is friction-free, and there is no appreciable air resistance. What is the speed of the bead at point C?

Answer 16

34 m/s

Question 17

A certain battery charger uses 12 W of power. At 6.0 cents per kilowatt-hour, how much does it cost to charge batteries for a full day?

Answer 17

1.7 c

Question 18

In the product A ∙ B ∙ C, A has 5 significant figures, B has 2 significant figures, and C has 3 significant figures. How many significant figures does the product have?

Answer 18

2

Question 19

If the answer to your calculation has units of kg ∙ m2/s, what type of quantity could it be? (There could be more than one correct choice).

Answer 19

angular momentum

Question 20

Two objects of different mass have equal, non-zero kinetic energies. Which object has the greater magnitude momentum?

Answer 20

the heavier object

Question 21

A tiger is running in a straight line. If we double both the mass and speed of the tiger, the magnitude of its momentum will increase by what factor?

Answer 21

4

Question 22

A rocket explodes into two fragments, one 25 times heavier than the other. The magnitude of the momentum change of the lighter fragment is

Answer 22

The same as the momentum change of the heavier fragment.

Question 23

You are standing on a skateboard, initially at rest. A friend throws a very heavy ball towards you. You have two choices about what to do with the ball: either catch the ball or deflect it back toward your friend with the same speed as it was originally thrown. Which choice should you make in order to maximize your speed on the skateboard?

Answer 23

Deflect the ball back.

Question 24

In the figure, determine the character of the collision. The masses of the blocks, and the velocities before and after, are shown. the collision is

Answer 24

completely inelastic.

Question 25

A very elastic rubber ball is dropped from a certain height and hits the floor with a downward speed v. Since it is so elastic, the ball bounces back with the same speed v going upward. Which of the following statements about the bounce are correct? (There could be more than one correct choice).

Answer 25

The magnitude of the ball’s momentum was the same just before and after the bounce.

Question 26

In an inelastic collision involving an isolated system, the final total momentum is

Answer 26

exactly the same as the initial momentum

Question 27

In the figure showing an isolated system, determine the character of the collision. The masses of the blocks, and the velocities before and after, are shown. the collision is

Answer 27

not possible because momentum is not conserved.

Question 28

Identical forces act for the same length of time on two different objects. The magnitude of the change in momentum of the lighter object is

Answer 28

exactly equal to the magnitude of the change in momentum of the larger mass.

Question 29

A 2.0-kg ball moving eastward at 3.0 m/s suddenly collides with and sticks to a 4.0-kg ball moving northward at 2.0 m/s. What is the magnitude of the momentum of this system just after the collision?

Answer 29

10 kg m/s

Question 30

An 8.0-g bullet is suddenly shot into a 4.0-kg block that is at rest on a frictionless horizontal surface as shown in the figure. The bullet remains lodged in the block. The block then moves against a spring and compresses it by 3.7 cm. The force constant (spring constant) of the spring is 2500 N/m. What is the initial speed v of the bullet?

Answer 30

460 m/s

Question 31

A block of mass m - 34 kg and speed v is behind a block of mass M = 81 kg and speed of 0.50 m/s, as shown in the figure. The surface is frictionless and the blocks collide and couple. After the collision, the blocks have a common speed of 0.90 m/s. What is the magnitude of the impulse on the 34-kg block due to the collision?

Answer 31

32 N * s