Phys Exam 2

Suppose a ball of putty moving with 1 kg⋅m/skg⋅m/s of momentum collides with and sticks to an identical ball of putty moving perpendicular to the first one with 1 kg⋅m/skg⋅m/s of momentum. What is the magnitude of their combined momentum?

1.41 kg(m)/s

Suppose the potential energy of a drawn bow is 50 joules and the kinetic energy of the shot arrow is 40 joules. Then...

10 Joules go to warming the bow.

Carl is pushing a box towards the right with a 10N force, but the box does not move. a) What is the direction and magnitude of static friction force?

10 N to the left

Part complete What will be the kinetic energy of a pile driver ram starting from rest that undergoes a 10-kJkJ decrease in potential energy?

10 kJ

Carl is pushing a box towards the right with a 10N force, but the box does not move. b) To try to get it to move, Carl pushes with a larger force of 15 N, but he is still unable to move the box, what is now the static friction force between the box and the ground?

15 N

A soccer player kicks a ball with 1500 N of force. The force from the ball on the foot is...

1500 N

Calculate the kinetic energy of a 94-kgkg scooter moving at 18 m/sm/s.

15000J

If the box is now being pushed towards the right at constant speed with a 20 N force, a) what is the magnitude and direction of the kinetic friction force?

20 N to the left

In an ideal pulley system, a person can lift a 100N crate by pulling the rope downward with a force of 20 N. For every 1-meter she pulls downward, the crate rises.

25 cm

If you push a crate horizontally with 100 NN across a 10-mm factory floor and friction between the crate and the floor is a steady 70 NN, how much kinetic energy is gained by the crate?

300J

What impulse occurs when an average force of 15 NN is exerted on a cart for 2.4 ss?

36 kg(m)/s

Part complete When the useful energy output of a simple machine is 100 J, and the total energy input is 200 J, the efficiency is _______.

50%

Part complete If an input of 100 J in a pulley system increases the potential energy of a load by 60 J, what is the efficiency of the system?

60%

Rank Potential Energy from greatest to least

A, E, C, B, D

Part complete How do linear momentum and angular momentum differ?

Angular momentum depends on the distribution of mass, whereas linear momentum depends on the total mass

Rank the cups by the amount they depart from a straight-line path (most curved to least curved).

B, C, A

Rank the torque needed to keep the stick steady, from largest to smallest.

B, C, A

Consider a bus colliding head on with a flying bug. The force of impact splatters the bug over the windshield while the bus suffers no damage whatsoever. what force is greater?

Both forces are the same

When traveling twice as fast your kinetic energy is increased _______.

By four times

Part complete Rank speed from greatest to least at each point.

D, B, C, E, A

Rank Kinetic Energy from greatest to least

D, B, C, E, A

systems of units are necessary to communicate data, so it is important to understand, be able to identify, and use them properly. b) Indicate which of the following are derived units and which ones multiple/submultiples. Unit: Newton: Millimeter: Gram: Joule: km:

Derived, Multiple, Multiple, Derived, Multiple

When the speed of an object is doubled, its momentum

Doubles

Part complete What is required to change the angular momentum of a system?

External torque

An ostrich egg of mass mm travelling at a speed vv hits a sagging bed sheet and is brought to rest in a time tt. b) Part complete If the mass of the egg is 1.5 kgkg, its initial speed is 2.3 m/sm/s, and the time to stop is 0.20 ss, find the average force on the egg.

F= 17N

An ostrich egg of mass mm travelling at a speed vv hits a sagging bed sheet and is brought to rest in a time tt. a) Find the force which brings the egg to rest upon hitting the sheet.

F=mv/t

Part complete The torque exerted by a crowbar on an object increases with increased _______.

Force and leverage distance

When you lift twice the load twice as high, in half the time, the increase in potential energy is _______.

Four times

Freight car A is moving towards a identical freight car B that is at rest. When they collide, both freight cars couples together. Compare with the initial speed of freight car A, the speed of the coupled freight cars is...

Half

The apple-orange system will move with constant speed

If a force equal and opposite to the friction force on the apple's feet occur.

systems of units are necessary to communicate data, so it is important to understand, be able to identify, and use them properly. a) All the following units are part of the international system (IS) except for:

Inch

Part complete How does the force needed to turn the wrench change if you increase the lever arm?

It decreases

Part complete How does the lever arm change if you decrease the angle of the force?

It decreases

Part complete How does the lever arm change when you decrease the distance to the nut?

It decreases

Two cars of the same mass are travelling at 20m/s, when they apply the brakes and come to a full stop. The first car stops in 20m while the second car stops in 25m. How does the work done by the brakes of these cars compare.

It is the same

Consider a dish falling on a carpet vs a hard floor, the change in momentum will be...

It is the same in both cases

when you hop off a curb, Earth pulls you downward. Why doesn't the earth move towards you?

It moves, but by an imperceptible amount

How much impulse stops a 50-kgkg carton sliding at 4.0 m/sm/s when it meets a rough surface?

J= 200 N(s)

80-kgkg person sits 2.0 mm from the center of a horizontally rotating platform with a tangential speed of 2.0 m/sm/s. What is the angular momentum of the person?

L =320 kg⋅m2/s

Part complete In which is momentum conserved: an elastic collision or an inelastic collision?

Momentum is conserved in elastic and inelastic collisions.

Carl is pushing a box towards the right with a 10N force, but the box does not move. c) if the box's mass is m=5kg and carl needs to apply a minimum force of 24 N to move the box, what is the statice friction coefficient between the box and the floor.

Ms = 0.48

If the box is now being pushed towards the right at constant speed with a 20 N force, b) what is the kinetic friction coefficient? The box's mass is 5kg.

Ms= 0.4

Two people, initially at rest on slippery ice, push each other off. Will they move at the same speed in opposite directions?

Only if the masses are equal

A car hoisted in a service station has, relative to the floor, a potential energy that is:

Positive

If the forces that act on a cannonball and the recoiling cannon from which it is fired are equal in magnitude, why do the cannonball and cannon have very different accelerations?

Remember F = ma, and note that the cannon has a much greater mass than the cannon ball, so the cannon accelerates less for the same force.

Part complete How is rotational inertia similar to inertia as studied in previous chapters?

Rotational inertia is the resistance to a change in rotational motion, which is similar to inertia which is a resistance to a change in velocity.

Part complete Calculate the torque produced by a 48-NN perpendicular force at the end of a 0.18-mm-long wrench.

T= 8.6 N(M)

If the mass of a sliding block is tripled while the applied net force is kept the same, by how much does the acceleration change?

The acceleration is reduced to 1/3 of its original value.

A boxer can hit a heavy bag with great force. Why can't he hit a piece of tissue paper in midair with the same amount of force?

The boxer can only hit the tissue paper with a force as large as the tissue paper can exert on the boxer, and the low-mass tissue can only exert a weak force.

Part complete How does the angular momentum of a cat change in falling from a tree?

The cat rotates its body through an angle, but the angular momentum of the cat remains constant.

Car A travelling at twice the speed of car B. If both cars stop in the same distance, how much more force do the brakes in car A compare to the brakes in car B.

The force is four times larger

if the mass of a sliding block is tripled, what must happen to the force for the acceleration to remain constant?

The force must triple

The centers of gravity of the three trucks parked on a hill are shown by the Xs. Which truck(s) will tip over?

The left truck

When a cannon is fired, the accelerations of the cannon and cannonball are different because...

The masses are different

If the system is considered to be the apple and the orange together (Figure 1), is there a net force on the system when the apple pulls (ignoring friction with the floor)?

The net force is zero because the action and reaction forces are internal to the system.

Consider hitting a baseball with a bat. If we call the force on the bat against the ball the action force, identify the reaction force.

The reaction force is the force by the ball on the bat.

When one does twice the work in twice the time, the power expended is _______.

The same

Part complete When you whirl a can overhead by a string in a circular path, what is the direction of the force exerted on the can?

Toward the center of the circle.

A slow gradual pull on the bottom of a string results in the top string breaking. Is this (That the top string breaks as opposed to the bottom string) related to the ball's weight or only to its mass?

Weight

must a car with momentum have kinetic energy?

Yes

you push a stationary brick wall for several minutes, which of the following is true?

You do not do mechanical work on the wall

The center of gravity of a basketball is located _______.

at its geometrical center

a certain machine is 30% efficient. This means that the machine

converts 30% of the energy input to useful work-- 70% of the energy input will be wasted

Energy cannot be _______.

destroyed

when the force that produces an impulse act for twice as long, the impulse is...

doubled

Compare with a lightweight glider, a heavier glider would have to push air

downward with greater force

A boxer rides with the punch so as to reduce _______.

force

Part complete The work that is done when twice the load is lifted twice the distance is _______.

four times as much

The tangential speed on the outer edge of a rotating carousel is _______.

greater than toward the center

work is done lifting a barbell against its weight. If you lift a barbell, that is half as heavy, to the same height, then the work you do is:

half as much

Cassy can get more force on the bricks she breaks with a blow of her bare hand when _______.

her hand is made to bounce from the bricks.

A slowly moving ship can have a greater momentum than a fast-moving racing car when _______.

its mass times velocity is greater than that of the car.

The rock and meterstick balance at the 25-cmcm mark, as shown in (Figure 1). The meterstick has a mass of 1.6 kgkg. What must be the mass of the rock?

m=1.6 kg

What is the momentum of an 9.0-kgkg bowling ball rolling at 2.8 m/sm/s ?

p= 25 kg(m)/s

A job can be done slowly or quickly. If both cases, the same amount of work is required, then they require a different amount of what?

power

The quantity that is called impulse can be measured by the _______.

product of force and time.

Part complete When a big fish swims into an oncoming smaller fish and swallows it, the momentum of the two-fish system _______.

remains the same.

you do work when pushing a cart to move it a certain distance: b) If you push the cart twice as far with half the force, then the work you do it:

the same

you do work when pushing a cart to move it a certain distance: a) if you push the cart twice as far with the same force, then the work you do is:

twice as much

A 5.0-kgkg fish swimming 0.50 m/sm/s swallows an absentminded 1.0-kgkg fish swimming toward it at a speed that brings both fish to a halt immediately after lunch. Find the speed of the approaching smaller fish before lunch.

v=2.5 m/s

If a trapeze artist rotates once each second while sailing through the air and contracts to reduce her rotational inertia to one-third of what it was, how many rotations per second will result?

w= 3 rotations per second

When two vehicles collide, momentum is conserved _______.

whether the collision is elastic or inelastic.

when you hop off a curb, Earth pulls you downward. The reaction to this force is...

you pulling Earth upward