PHYS 121 - Question Bank for Exam 2

An object moves in a circular path at a constant speed. What is the relationship between the directions of the object's velocity and acceleration vectors?

The velocity and acceleration vectors are perpendicular.

An object moves in a circular path at a constant speed. What is the direction of the net force acting on the object?

The net force is directed toward the center of the circular path.

Why does a satellite in a circular orbit travel at a constant speed?

There is no component of force acting along the direction of motion of the satellite.

Two objects attract each other gravitationally. If the mass of each object doubles, how does the gravitational force between them change?

The gravitational force increases by a factor of 4

Earth's orbit around the Sun is slightly elliptical. Thus, Earth actually gets closer to the Sun during part of the year. What happens to Earth's orbital speed when it is closer to the Sun?

Earth's orbital speed is greater when it is closer to the Sun than when it is farther from the Sun.

Suppose the speed of a car is 11.1 m/s while traveling

A ball is thrown straight upward. How does the sign of the work done by gravity while the ball is traveling upward compare with the sign of the work done by gravity while the ball is traveling downward?

Work done by gravity is negative while the ball is traveling upward and positive while the ball is traveling downward.

A graph depicts force versus position. What represents the work done by the force over the given displacement?

The work done is equal to the area under the curve.

If the net work done on an object is zero, what can you determine about the object's kinetic energy?

The object's kinetic energy remains the same.

Two objects are moving at equal speed along a level, frictionless surface. The second object has twice the mass of the first object. They both slide up the same frictionless incline plane. Which object rises to a greater height?

The two objects rise to the same height.

Two identical balls are thrown vertically upward. The second ball is thrown with an initial speed that is twice that of the first ball. How does the maximum height of the two balls compare?

The maximum height of the second ball is four times that of the first ball.

An object weighing 20 N moves horizontally toward the right a distance of 5.0 m. What is the work done on the object by the force of gravity?

The work done on the object by the force of gravity is zero joules.

Person B does twice the work of person A, and in one-half of the time . How does the power output of person B compare to person A?

Person B has half the power output of person A.

What represents the impulse of the force in a graph of force versus time?

The impulse is equal to the area under the curve.

In a lab environment, you are investigating the impulse of a force exerted on a brick when the brick's speed is reduced from 2.5 m/s to a complete stop. First, you allow the brick to slam into a secured piece of wood, bringing the brick to a sudden stop. Second, you allow the brick to plow into a large slab of gelatin so that the brick comes to a gradual halt. In which situation is there a greater impulse of the force on the brick?

The impulse is the same in both situations.

A lump of putty and a rubber ball have equal mass. Both are thrown with equal speed against a wall. The putty sticks to the wall. The ball bounces back at nearly the same speed with which it hit the wall. Which object experiences the greater momentum change?

The ball experiences the greater momentum change.

For an elastic collision, which of the following statements are true?

Momentum is conserved, Kinetic energy is conserved.

A freight car moves along a frictionless level railroad track at constant speed. The freight car is open on the top. A large load of sand is suddenly dumped into the freight car. What happens to the speed of the freight car?

The speed of the freight car decreases.

a) A 1200 kg car executes uniform circular motion around a track of radius 60m. If the car goes once around in 30 seconds, without slipping, determine the force of static friction on the car.

b) Determine the maximum speed of the car, before it slips (skids out).

a) 3160 N, inward

b) 13.7 m/s

IN a 1901 circus performance, Allo “Dare Devil” DIavolo introduced the stunt of riding a bicycle in a loop-the-loop. Assuming the loop is a cirucle with radius R = 2.7m, what is the least speed v Diavolo could have at the top of the loop to remain in contact with it there?

5.1 m/s

A race car starts from rest and reaches a speed of 35 m/s in 11s while moving on a circular track of radius 500m. Assuming constant tangential acceleration, find:

a) Magnitude of the Tangential acceleration

b) Radial acceleration as the instant when v= 15m/s

c) The magnitude of the Total Acceleration at that same instant

a) 3.2 m/s²

b) 0.45 m/s²

c) 3.23 m/s²

a) Find the net force on a 1.5×10⁶ kg asteroid which is positioned halfway between the Earth and the moon. b) Then, find it’s acceleration. (M_earth=5.98×10²⁴kg, M_moon=7.35×10²²kg. Avg. Dist = 3.84×10⁸m)

a) -16000 N

b) -0.011 m/s²

a) The earth orbits once around the sun 365.25 days. Assuming a nearly circular orbit, determine the orbital speed (v) of the earth? b) Also determine earth’s centripetal acceleration (a_R).

a) 25800 m/s

b) 0.00594 m/s²

The 1 kg hammer head comes to rest after driving a nail a distance of 4 cm deep into a soft wooden board with a single blow. The initial speed of the hammer head was a 6.32 m/s. Determine the average force of the hammer on a nail.

500N

Your chemistry lab partner, holding a test tube of HCl, looses her grip, and it free falls to the floor. She drops the acid from a height of 2m, and it comes to rest (upon striking the floor) in a distance of 0.1 m — crumbling as it hits. The mass of the system is 0.15 kg. Determine the force with which it strikes the floor.

31N

A red ball with a velocity of +3.0 m/s collides head-on with a yellow ball of equal mass moving with a velocity of −2.0 m/s. What is the velocity of the two balls after the elastic collision?

The velocity of the red ball is −2.0 m/s; the velocity of the yellow ball is +3.0 m/s.

When a person steps forward out of a small boat onto a dock, the boat recoils backward in the water. Why does this occur?

The total momentum of the system is conserved.

Suppose the speed of a car is 11.1 m/s while traveling up, over a hill with a radius of curvature of 25m, and the mass of the car is 1200 kg. Determine the a) centripetal acceleration of the car, b) net force acting on the car, c) the speed where centripetal force would equal the force of gravity.

a) 4.928 m/s²

b) 5914.08 N

c) 15.65 m/s

The game of tetherball is seen on playgrounds across the world. It consists of a vertical pole with a ball attached to the top via a (massless) rope. THe ball has a weight of W = 4.5N and is sent across the pole in a horizontal circular path, ad the rope has a length of L = 2.0m and makes an angle of θ = 30 with respect to the pole. a) What is the tension in the rope? b) With what speed does the ball circle the pole? c) How long does it take for the ball to make one revolution?

a) 5√3 N or 5.196 N

b) 2.379 m/s

c) 2.64 sec

Two blocks with masses m_A and m_B, are connected to each other and to a central post by thin rods. The blocks revolve about the post at the same frequency f on a friction-less horizontal surface at distance r_A and r_B from the post. Show that the force of tension in block A is:

F_TA = 4π² (m_Ar_A + m_Br_B)

F_TA = 4π² (m_Ar_A + m_Br_B)

If a curve with a radius of 95 m is properly banked for a car traveling 65 km/hr, what must be the coefficient of static friction for a car not to skid when traveling at 95 km/h?

0.33

True or False: Acceleration, velocity, and net force pint toward the center of uniform circular motion.

False

a) Draw a FBD of below program

b) A car with mass M is merging onto the interstate on a banked curve with radius r. The curve is banked at an angle

Two objects attract each other gravitationally with a force of 2.5×10^-10N when they are 0.25m apart. Their total is 4.0 kg. Find their individual masses.

3.94, 0.06 kg

A woman (m = 55kg) flying a plane executes a loop of radius 380m while flying at 65 m/s. Determine the value of the centripetal force acting on the woman when at the top of the loop. b) What is the apparent weight of the woman at this location? c) How fast would the woman need to be going in order to have an apparent weight equal to her actual weihgt?

a) 611.51 N

b) 72.51 N

c) 86 m/s

A curve of radius 78m is banked for a design speed of 85 km/h. If the coefficient of static friction is 0.30 (wet pavement), at which range of speeds can a car safely make the curve?

V_min = 59.08. km/hr

V_max = 114 km/hr

What is teh minimum work needed to push a 950 kg car 710m up along a 9.0° incline? Ignore friction.

1.02 ×10⁶ J

A box of mass 4.0 kg is accelerated from rest by a force across a floor at a rate of 2.0 m/s² for 7.0s. Find the net work done on the box.

392 J

A 1200N crate rests on the floor. How much work is required to move it at a constant speed a) 5.0m along the floor against a frictional force of 230N, and b) 5.0m vertically? c) Should these forces be the same? Why or why not?

a) 1150 J

b) 6000 J

c) No

A 265 kg load is lifted 18.0 m vertically with an acceleration a = 0.160g by a single cable. Determine a) the tension in the cable, b) the net work done on the load, c) the work done by the cable on the load, d) the work done by gravity on the load.

a) 3012.52 N

b) 7479.36 J

c) 54225.36 J

d) -46.746 J

If it requires 6.0J of work to stetch a particular spring by 2.0 cm from its equilibrium length, how much work will be required to stretch it an additional 4.0 cm?

48 J

An 85g arrow is fired from a bow whose string exerts an average force of 105 N on the arrow over a distance of 75 cm. What is the speed of the arrow as it leaves the bow?

43.05 m/s

If the kinetic energy of a particle is tripled, by what factor has it speed increased? b) If the speed of a particle is halved, by what factor does its kinetic energy change?

√3

A 75.0 kg firefighter climbs a flight of stairs 28.0m high. How much work does he do? If the same firefighter walks up a hill that is at an angle of 22°, how much work does he do?

20580 J

True or False: The orbital velocity of a satellite does not depend on the mass and radius of the satellite.

True

A highway curve has a radius of 80m and is banked at an angle of 12°. A car travels around the curve at a speed of 15 m/s. Determine whether the car can make the turn without friction.

12.9 m/s < 215 m/s = car will not be able to take turn without friction

A communication satellite is placed in a circular orbit around Eart at a distance of 3.5×10⁷ from the center of Earth. Calculate the orbitial period of the satellite and determine whether it is in a geosynchronous orbit (M_E = 5.98×10²⁴ kg, G = 6.67×10^-11Nm²/kg²)

T = 6.51×10⁴ seconds —> 18.1 hours = Not in geosynchronous orbit