Exam 2 Review

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1) Draw a free-body diagram for the following scenarios:

a. An elevator is moving downwards and is slowing down:

b. An elevator is moving downwards and is speeding up:

c. An elevator is moving up and slowing down:

d. An elevator is moving down and speeding up:

e. A car is dragged up a hill that is 30 degrees above the horizontal and it is

accelerating up the hill.

2) A box is hanging from a massless string that is attached to the ceiling. The box has a

mass of 25 kg, what is the tension in the string?

3) Consider the following drawing:

If the weight of the ball is 150 N, which of the following is true?

a. T > 150 N

b. T < 150 N

c. T = 150 N

4) A croquet player hits a ball with a mass of 50 g at a speed of 3 m/s. The grass exerts a

frictional force of 0.02 N on the ball. Will the ball reach the desired hoop that is 10

meters away?

5) A box is speeding up horizontally due to being pulled by a tension T. The kinetic friction

acting on the box is 25 N, while the acceleration of the box is 18 m/s^2. We also know

that the normal force is equal to 147 N. What is the tension in the rope?

6) Jack has a mass of 58 kg. He is standing on a scale in an elevator that is accelerating

downward at 1.7 m/s^2. What is the reading on the scale?

7) A 35 kg ceiling light is suspended 2 meters below the ceiling by two cables that are each

30 degrees from the vertical. What is the tension in each cable?

8) An astronaut has a weight of 800 N on Earth. What is his weight on Mars, where g = 3.76

m/s^2?

9) What is the minimum downward force (F) on the box shown below that will keep it from

slipping? The coefficients of static and kinetic friction between the box and the floor are

0.35 and 0.25, respectively.

10) A 6 kg boy is sitting on a hill that has a 15 degree angle with the horizontal. What is the

magnitude of the normal force exerted by the hill on the boy?

11) What is the tension of the rope in the following drawing?

12) What is the normal force acting on the 100 kg block in the following drawing?

13) Two workers are sliding a 300 kg crate across the floor. One worker pushes forward on

the crate with a force of 380 N, while the other pulls in the same direction with a force of

350 N using a rope connected to the crate. Both forces are horizontal, and the crate slides

at a constant velocity. What is the crate’s coefficient of kinetic friction on the floor?

14) A car skids to a stop in 50 m starting at 20 m/s. The coefficient of static friction between

the person and the seat is 0.5, while the kinetic coefficient is 0.3. If there is a 20 kg

passenger on the seat, will they slip off the seat due to the sudden breaking?

15) Draw the net force vs time curve based on the following curve:

16) When dealing with forces, acceleration and net force will always point in:

a. Opposite directions

b. The same direction

c. Not related to each other

17) Find the normal force of the following scenarios:

a.

b.

18) Two blocks are at rest on a frictionless incline, as is shown below. What are the tensions

in the 2 strings?

19) Use the picture below for the following question: The ramp below is frictionless. Block

M has a mass of 10 kg and block m has a mass of 5 kg, and the angle theta is 40 degrees.

If the two blocks are released from rest, what direction will the 10 kg block travel, and

what will be the magnitude of its acceleration?

20) Two blocks are connected by a string using a frictionless pulley as shown below. What is

the acceleration of the upper block if the coefficient of kinetic friction between it and the

ground is equal to 0.2?

CIRCULAR MOTION

21) What is the formula for centripetal acceleration?

22) What is the formula that relates Period to frequency?

23) What is a formula that relates period to velocity? How about frequency to velocity?

24) What is another way to write ∑F = ma ?

25) What is the formula for force due to gravity?

26) Label the following on each of the four points of the circle below: Velocity, Net Force,

and Centripetal Acceleration.

27) If a circle of a certain radius and velocity has a period of 4 seconds, what is the

frequency?

28) An audio CD has a diameter of 120 mm and spins up to 540 rpm. When a CD is spinning

at its maximum rate, how much time is required for one revolution? If a speck of dust

rides on the outside edge of the disk, how fast is it going? What is the acceleration?

29)

30) A car is moving at a constant speed down the road, when it reaches a semi-circular dip in

the road. At the very bottom of the dip, which of the following must be true?

a. The normal force is greater than the weight

b. The weight is greater than the normal force

c. The weight and the normal force are equal to each other to maintain balance

31) A car is moving at a constant speed when it reaches a hill that is circular. When the car

reaches the peak of the hill, which of the following is true?

a. The normal force is greater than the weight

b. The weight is greater than the normal force

c. The weight and the normal force are equal to each other to maintain balance

32) A car is turning a corner at a constant speed, following the segment of a circle. Which

force is providing the centripetal acceleration?

33) A man attaches a 5 meter rope to a shopping cart that has a mass of 20 kg. He grabs the

free end of the rope and starts to spin the shopping cart around himself, keeping the rope

parallel to the ground. If the tension in the rope is 110 N, how much time does it take for

the cart to make one whole rotation?

34) A ball that is attached to a string is being spun around in a vertical circle at a constant

speed. Which of the following is true?

a. The ball’s acceleration is zero because the speed is constant

b. The ball’s velocity is constant

c. The ball has a nonzero acceleration and a non-constant velocity

35) On a train ride in an amusement park, the train travels around in a small 5 meter radius

circle for the children to enjoy. For safety, the max acceleration that the riders may

experience is 20 m/s^2.

a. What is the period of the ride when it is being operated at the maximum

acceleration?

b. How fast are the riders moving when the ride is operated at this period?

36) What is the maximum speed with which a 2000 kg car can make a turn around a curve of

a radius 15 m on a level (unbanked) road without sliding? The coefficient of static

friction is 0.1 and the coefficient of kinetic friction is 0.05.

37) A curve on a racetrack with a radius of 55 meters is banked at an angle of 20 degrees

from the horizontal. At which speed can the car take the turn without assistance from

friction?

38) The passengers on a roller coaster feel 50% heavier than their true weight as their cart

goes through a dip with a 30 m radius of curvature. What is the car’s speed at the bottom

of the dip?

39) The centers of a 10 kg ball and a 200 g ball are separated by 15 cm. What gravitational

force does each exert on the other?

40) A motorcyclist in the Globe of Death, shown below, rides in a 2.2 m radius vertical loop.

What is the minimum speed at which the rider can take the loop?

41) Planet 1 has a free-fall acceleration of 5 m/s^2 at the surface. Planet 2 has two times the

mass and 1/4 the radius of planet 1. What is the acceleration due to gravity on planet 2?

42) The gravitational force between two giant lead spheres in 0.01 N when the centers of the

spheres are 20 m apart. What is the distance between their centers when the gravitational

force between them is 0.16 N?

43) You are 0.65 m away from your classmate, and you both have 70 kg masses. What is the

gravitational force between you and your classmate?

44) What is the magnitude of the gravitational force of the earth on a 55 kg person? The mass

of the earth = 5.98 E 24 kg and the radius of the earth = 6.37 E 6 m.

45)

46) True or False: Objects in orbit are in free-fall.

47) A spacecraft has been sent to Mars in recent years. Mars is smaller than earth, and its

surface gravity is also lower. On mars, the free-fall acceleration is only 3.8 m/s^2. What

is the orbital period in minutes of a spacecraft in a low orbit near the surface of Mars?

The mass of Mars = 6.39 E 23 kg and the radius of Mars = 3.397 E 6 m.

48) An earth satellite moves in a circular orbit at a speed of 5500 m/s. What is the orbital

period? Earth mass = 5.972 E 24 kg and the radius = 6.371 million m.