HW Unit 2 Review Chp 5-7

In a physical fitness program, a woman who weighs 510 N runs up four flights of stairs in 22 s. Each flight rises 3.1 m. (1 hp = 746 W)(a) What is her total change in potential energy?(b) What was the minimum average power (in watts) that she expended during the 22 s?(c) What horsepower motor would be required to generate the same power?

(a) 6324 j (b) 287 watts (c) 0.39 HP

A 0.12-kg block is held in place against the spring by a 35-N horizontal external force. The external force is removed, and the block is projected with a velocity when it separates from the spring, as shown in the figure. The block descends a ramp and has a velocity at the bottom of the ramp. The track is frictionless between points A and B. The block enters a rough section at B, extending to E. The coefficient of kinetic friction between the block and the rough surface is 0.26. The block moves on to D, where it stops. By how many centimeters was the spring initially compressed?

0.49 cm

A 0.14-kg baseball is dropped from rest from a height of 2.0 m above the ground. What is the magnitude of its momentum just before it hits the ground if we neglect air resistance?

0.88 kg ∙ m/s

A 2.0-kg ball is moving with a constant speed of 5.0 m/s in a horizontal circle whose diameter is 1.0 m. What is the magnitude of the net force on the ball?

100N

A force acts on an object, causing it to move parallel to the force. The graph in the figure shows this force as a function of the position of the object. How much work does the force do as the object moves from 0 to 15 m?

125J

The captain of a spaceship orbiting planet X discovers that to remain in orbit at from the planet's center, she needs to maintain a speed of 68m/s What is the mass of planet X? (G = 6.67 × 10-11 N ∙ m2/kg2)

2.8 × 10^19 kg

A dinner plate falls vertically to the floor and breaks up into three pieces, which slide horizontally along the floor. Immediately after the impact, a 320-g piece moves along the +x-axis with a speed of 2.00 m/s and a 355-g piece moves along the +y-axis with a speed of 1.50 m/s. The third piece has a mass of 100 g. In what direction relative to the +x-axis does the third piece move?

219.8° from the +x-axis

Two astronauts, of masses 60 kg and 80 kg, are initially right next to each other and at rest in outer space. They suddenly push each other apart. What is their separation after the heavier astronaut has moved 12 m?

28M

How much kinetic energy does a 0.30-kg stone have if it is thrown at 44m/s

290 J

When you drop a pebble from height H, it reaches the ground with kinetic energy K if there is no air resistance. From what height should you drop it so it will reach the ground with twice as much kinetic energy?

2H

A very light ideal spring having a spring constant (force constant) of 8.2 N/cm is used to lift a 2.2-kg tool with an upward acceleration of 3.25 m/s2. If the spring has negligible length when it us not stretched, how long is it while it is pulling the tool upward?

3.5 CM

Mithra is an unknown planet that has two moons, A and B, in circular orbits around it. The table summarizes the hypothetical data about these moons. What is the magnitude of the maximum gravitational force that Moon A exerts on Moon B? (G = 6.67 × 10-11 N ∙ m2/kg2)

4.0 × 10^14 N

When you drop a pebble from height H, it reaches the ground with speed V if there is no air resistance. From what height should you drop it so it will reach the ground with twice speed?

4H

Two planets have the same surface gravity, but planet B has twice the radius of planet A. If planet A has mass m, what is the mass of planet B?

4m

Which requires more work, increasing a car's speed from 0 mph to 30 mph or from 50 mph to 60 mph?

50 mph to 60 mph

The earth has radius R. A satellite of mass 100 kg is in orbit at an altitude of 3R above the earth's surface. What is the satellite's weight at the altitude of its orbit?

61 N

At a given point above Earth's surface, the acceleration due to gravity is equal to 7.8m/s^2 What is the altitude of this point above Earth's surface? (G = 6.67 × 10-11 N ∙ m2/kg2, M earth = 5.97 × 1024 kg, R earth = 6.38 × 106 m)

770K

A block of mass m = 9.0 kg and speed V and is behind a block of mass M = 27 kg and speed of as shown int the figure. The surface is frictionless, and the blocks suddenly collide and couple. After the collision, the blocks have a common speed of 0.90 m/s. How much kinetic energy of the blocks is lost due to the collision?

8.6 J

Two astronauts, of masses 60 kg and 80 kg, are initially right next to each other and at rest in outer space. They suddenly push each other apart. How far has the heavier astronaut moved when the lighter astronaut has moved 12 m?

9.0 m

There must be equal amounts of mass on both sides of the center of mass (or center of gravity) of a system.

False

When you throw a pebble straight up with initial speed V, it reaches a maximum height H with no air resistance. At what speed should you throw it up vertically so it will go twice as high?

Square root 2 V

Let the orbital radius of a planet be R and let the orbital period of the planet be T. What quantity is constant for all planets orbiting the sun, assuming circular orbits?

T2/R3

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.)

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

A small car meshes with a large truck in a head-on collision. Which of the following statements concerning the magnitude of the momentum change during the collision is correct? (There could be more than one correct choice.)

The small car and the truck experience the same magnitude momentum change.

You throw a baseball straight up. Compare the sign of the work done by gravity while the ball goes up with the sign of the work done by gravity while it goes down.

The work is negative on the way up and positive on the way down.

A hypothetical planet has a mass of one-half that of the earth and a radius of twice that of the earth. What is the acceleration due to gravity on the planet in terms of g, the acceleration due to gravity at the surface of the earth?

g/8

You are making a circular turn in your car on a horizontal road when you hit a big patch of ice, causing the force of friction between the tires and the road to become zero. While the car is on the ice, it

moves along a straight-line path in its original direction.

A car goes around a circular curve on a horizontal road at constant speed. What is the direction of the friction force on the car due to the road?

perpendicular to the curve inward

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

the heavier object

A rubber ball bounces off of a wall with an initial speed v and reverses its direction so its speed is v right after the bounce. As a result of this bounce, which of the following quantities of the ball are conserved? (There could be more than one correct choice.)

the kinetic energy of the ball