Physics Midterm Review Unit 3

An artificial satellite orbits Earth at a speed of 7800 m/s and a height of 200 km above Earth's surface. The satellite experiences an acceleration due to gravity of

A 39 m/s2 B less than 39 m/s2 but greater than 9.8 m/s2 C 9.8 m/s2 D less than 9.8 m/s2 but greater than zero E zero

An object has a weight W when it is on the surface of a planet of radius R. What will be the gravitational force on the object after it has been moved to a distance of 4R from the center of the planet?

A 16W B 4W C W D 1/4W E 1/16W

A meteoroid is in a circular orbit 600 km above the surface of a distant planet. The planet has the same mass as Earth but has a radius that is 90 % of Earth's (where Earth's radius is approximately 6370 km). The acceleration of the meteoroid due to the gravitational force exerted by the planet is most nearly

A 9 m/s29 m/s2 toward the center of the planet B 9 m/s29 m/s2 in the direction of the meteoroid's motion C 10 m/s210 m/s2 toward the center of the planet D 10 m/s210 m/s2 in the direction of the meteoroid's motion

Picture of two circles with radius next to each other* Two solid spheres of radius R made of the same type of steel are placed in contact, as shown in the figures above. The magnitude of the gravitational force that they exert on each other is F1. When two other solid spheres of radius 3R made of this steel are placed in contact, what is the magnitude of the gravitational force that they exert on each other?

A F1 B 3F1 C 9F1 D 81F1

Picture of man swinging ball* A student swings a ball on a light rod at a constant speed in a vertical circle, as shown in the figure. Which of the following correctly ranks the magnitudes of the forces exerted by the rod on the ball F1, F2, F3, and F4 when the ball is at locations 1, 2, 3, and 4, respectively?

A F1=F2=F3=F4 B (F2=F3)>F4>F1 C F4>F1>(F2=F3) D F1>F4>(F2=F3)

An astronaut with mass MA is within a satellite that orbits Earth at a height H above its surface. Earth has a mass ME and radius RE. Which of the following is a correct expression for the gravitational force exerted on the astronaut by Earth?

A Fg=GMgMA/H2 B Fg=GMgMA/R2E C Fg=GMgMA/(RE+H)2 D Fg=0

Picture of cart going downhill* A cart of mass m rolls past the circular bottom of a hill (point P). Which of the following statements about the normal force Fn exerted on the cart at point P is correct?

A Fn=mg, because the normal force on an incline is equal to mgcosθ and θ=0 at point P. B Fn=mg, because the speed of the cart is neither increasing nor decreasing at point P. C Fn is equal to the centripetal force on the cart at point P, because only the track can exert a force toward the center of the circle. D Fn is greater than mg at point P, because the cart is experiencing an upward acceleration.

picture of circle with car next to it* The toy car shown in the figure above enters the vertical circular loop with an initial velocity and moves completely around the loop without friction. If the car has no means of self-propulsion, which of the following is true of the car's acceleration at the instant it is at point P ?

A It is vertically upward. B It is in the direction of the velocity. C It is directly toward the center of the circle. D It has components both downward and toward the center of the circle. E It has components both downward and away from the center of the circle.

A student must design an experiment to determine the gravitational mass of an object. Which of the following experiments could the student use? Select two answers.

A Place the object on one side of a lever at a known distance away from a fulcrum. Place known masses on the other side of the fulcrum so that they are also placed on the lever at known distances from the fulcrum. Move the known masses to a known distance such that the lever is in static equilibrium. B Place the object on a surface of negligible friction, and pull the object horizontally across the surface with a spring scale at a nonconstant speed such that a motion detector can measure how the object's speed as a function of time changes. C Place the object on a surface that provides friction between the object and the surface. Use a surface such that the coefficient of friction between the object and the surface is known. Pull the object horizontally across the surface with a spring scale at a nonconstant speed such that a motion detector can measure how the object's speed as a function of time changes. D Place the object on the end of a vertically hanging spring with a known spring constant. Allow the spring to stretch to a new equilibrium position, and measure the distance the spring is stretched from its original equilibrium position.

Picture of planet with moon and 3 points between them* A spaceship travels from a planet to a moon and passes through the three positions A, B, and C, shown above. Position B is midway between the centers of the planet and the moon. The planet has a larger mass than the moon. At which location could the net gravitational force exerted on the spaceship be approximately zero?

A Position A B Position B C Position C D It cannot be determined without knowing the masses of the planet, the moon, and the spaceship, and the exact distance the spaceship is from the planet and the moon.

Picture of two circles with dot in the middle* Objects 1 and 2 have masses M1 and M2, respectively, where M1<M2. The objects are in outer space far away from any other objects, as shown above. Point PP is located halfway between their centers. At what location, if any, is the gravitational field due to the two objects equal to zero?

A Somewhere between object 1 and point P B At point P C Somewhere between point P and object 2 D The gravitational field due to the two objects is nonzero everywhere.

A moon orbits an isolated planet in deep space. Which of the following forces that the planet exerts on the moon can be considered as negligible?

A The electric force B The force due to gravity C Both the electric force and the force due to gravity D Neither the electric force nor the force due to gravity

An astronaut stands on the surface of an asteroid. The astronaut then jumps such that the astronaut is no longer in contact with the surface. The astronaut falls back down to the surface after a short time interval. Which of the following forces CANNOT be neglected when analyzing the motion of the astronaut?

A The electromagnetic force between the subatomic particles of the astronaut and the subatomic particles of the asteroid B The strong nuclear force between the subatomic particles of the astronaut and the subatomic particles of the asteroid C The weak nuclear force between the subatomic particles of the astronaut and the subatomic particles of the asteroid D The gravitational force between the astronaut and the asteroid

Picture of circle with ball and a data table* A student conducts an experiment in which a 0.5 kg ball is spun in a vertical circle from a string of length 1 m, as shown in the figure. The student uses the following equation to predict the force of tension exerted on the ball whenever it reaches the lowest point of its circular path at a known tangential speed for various trials. FTension=mv2r When the experiment is conducted, the student uses a force probe to measure the actual force of tension exerted on the ball. Why is the predicted force of tension different than the actual force of tension?

A The force probe has not been calibrated properly because the predicted tension forces are in agreement with their corresponding tangential speeds. B Not enough trials were conducted to observe the spread of uncertainty with the collected values because the predicted tension forces are in agreement with their corresponding tangential speeds. C The student did not account for the downward centrifugal force that occurs as a result of the inertia of the ball when it reaches the lowest point along its circular path. D The student did not account for the downward force due to gravity at the ball's lowest point along its circular path, so the predicted force of tension is the net centripetal force exerted on the ball.

Picture of planet and 2 moons around it* A planet has two moons, Moon A and Moon B, that orbit at different distances from the planet's center, as shown. Astronomers collect data regarding the planet, the two moons, and their obits. The astronomers are able to estimate the planet's radius and mass. The masses of the two moons are determined to be 2M for Moon A and M for Moon B. It is observed that the distance between Moon B and the planet is two times that of the distance between Moon A and the planet. How does force exerted from the planet on Moon A compare to the force exerted from the planet on Moon B ?

A The gravitational force exerted from the planet on Moon A is two times larger than the gravitational force exerted from the planet on Moon B . B The gravitational force exerted from the planet on Moon A is eight times larger than the gravitational force exerted from the planet on Moon B . C The gravitational force exerted from the planet on Moon A is two times smaller than the gravitational force exerted from the planet on Moon B . D The gravitational force exerted from the planet on Moon A is eight times smaller than the gravitational force exerted from the planet on Moon B .

A child has a toy tied to the end of a string and whirls the toy at constant speed in a horizontal circular path of radius R. The toy completes each revolution of its motion in a time period T. What is the magnitude of the acceleration of the toy?

A Zero B 4π2R / T2 C πR / T2 D g E 2πg

Picture of ball swinging around pole with a right triangle drawn* A ball of mass m is attached to a vertical rod by two massless strings. The rod is rotated about its axis so that both strings are taut, with tensions T1 and T2, respectively. The strings and rod form the right triangle shown in the figure above. The ball rotates in a horizontal circle of radius r with speed v. What is the tension T1 in the upper string?

A mg cos θ B mg sin θ C mg tan θ D mg/cos θ E mg/sin θ

Picture of ball swinging around pole with a right triangle drawn* A ball of mass m is attached to a vertical rod by two massless strings. The rod is rotated about its axis so that both strings are taut, with tensions T1 and T2, respectively. The strings and rod form the right triangle shown in the figure above. The ball rotates in a horizontal circle of radius r with speed v. What is the magnitude of the net force on the ball?

A mv2 / r B mg C T2 D T2 + mv2r E T1 + mg

Graph of tangential speed vs time* An object is spun in a horizontal circle such that it has a constant tangential speed at all points along its circular path of constant radius. A graph of the magnitude of the object's tangential speed as a function of time is shown in the graph. Which of the following graphs could show the magnitude of the object's centripetal acceleration as a function of time?

Horizontal straight line above the x axis; y-intercept = 9

Picture of circle with point x at the bottom* A stone disk is sliding on frictionless ice to the west with speed v, as shown in the figure above. As the disk slides by, a child uses a rubber mallet to hit the disk at point X, exerting a force directly toward the center of the disk. The child hits point X every half second for about 10 s, changing the trajectory of the disk but not causing it to rotate. Which of the following most closely approximates the path of the disk while the child is hitting it?

arrow going up left in parabolic path

Picture of cylinder contraption* A steel ball supported by a stick rotates in a circle of radius r, as shown above. The direction of the net force acting on the ball when it is in the position shown is indicated by which of the following?

arrow pointing towards center in dotted ring outline

Picture of 3 carts on 3 hills* The figures show a cart moving over the top of a hill (Case 1), moving at the bottom of a dip (Case 2), and moving at the top of a vertical loop (Case 3). In each case, the normal force acting on the car is Fn and the weight of the car is Fg. In which case is it always true that Fn>Fg, and in which case is it always true that Fn<Fg?

case 2; case 1