PRACTICE TEST

Bn Physics 125

FG = gravitational force, FG sin θ, etc., n or Fn = normal force, T or FT = tension force, μs, μk coefficients of static, kinetic friction fs = static friction, fk = kinetic friction (differentiate between these), Fp = push or pull m= mass, g = magnitude of acceleration of gravity on earth,9.8 m/s/s, v = speed, r = radius.

1. A net force is required to give an object with mass m an acceleration a. If a net force 6 is applied to an object with mass 2m, what is the acceleration on this object?

A) B) 2 C) 3 D) 4 E) 6

2. The figure shows the velocity versus time curve for a car traveling along a straight line. The car started from rest. Which of the following statements is FALSE?

A) No net force acts on the car during interval B.

B) Net forces act on the car during intervals A and C.

C) Opposing forces may be acting on the car during interval B.

D) Opposing forces may be acting on the car during interval C.

E) The car is traveling in a negative direction during intervalC.

3. A car enters a horizontal, curved roadbed of radius 50 m. The coefficient of static friction between the tires and the roadbed is 0.20. What is the maximum speed with which the car can safely negotiate the unbanked curve?

A) 5 m/s B) 10 m/s C) 20 m/s D) 40 m/s E) 100 m/s

4. An elevator suspended by a cab le is moving upward and slowing down. Which free-body diagram is correct?

5. The truck shown is moving to the right and slowing down due to friction. Which of the following is the correct free-body diagram?

a.

c.

b.d.

6. A small box sits on top of a large box, which is on the ground.

The free-body diagrams for the boxes areshown below.

TOP BOXBOTTOM BOX

The force of the bottom box on the top box(FBottom on Top ) is shown on the left free-body diagram . Which of the other forces shown best illustrates Newton’s 3rdLaw?

A. FG-TOP

B. FTOP ON BOTTOM

C. FN

D. FG-BOTTOM

E. None of the above

The next 2 questions refer to the block on the incline shown below:

7. The block of mass m is at rest on the ramp which is inclined at an angle of θ from horizontal. It is not on the verge of sliding. The magnitude of the frictional force on the block is:

A. µsmg D. mg cos θ

B. µsmg cos θ E. mg sin θ

C. µsmg sin θ

8. If the block were just about to slide (on the verge of sliding), what would be the magnitude of the frictional force on the block?

A. µsmg D. mg cos θ

B. µsmg cos θ E. a value between mg cos θ and mg sin θ

C. µsmg sin θ

The next 2 questions refer to the following situation. An 1800-kg Jeep travels along a straight 500-m portion of highway (from A to B) at a constant speed of 10 m/s. At B, the Jeep encounters astraight and level curve of radius 50 m. The Jeep follows the road from B to C traveling at a constant speed of 10 m/s while the direction of the Jeep changes from east to south.

9. What is the magnitude of the acceleration of the Jeep as it travels from B to C?

A) 2 m/s2 B) 5 m/s2 C) 10 m/s2 D) 20 m/s2 E) zero m/s2

10. What is the magnitude of the frictional force between the tires and the road as the Jeep negotiates the curve from B to C?

A) 9600 N B) 7200 N C) 3600 N D) 1800 N E) 1000 N

11. An object is traveling in uniform circular motion around the circle, in a clockwise direction.

a.What is the direction of the velocity vector at the instant the object passes the dot labeled 3?______

b. What is the direction of the acceleration vector at the instant the object passes the dot labeled 3?______

12. The graph at the right shows acceleration vs force graph for 3 objects. The mass of object 2 is 0.20 kg. You cannot just assume a1 = 1!. Find the mass of the objects 1 and 3.

Object 1: ______kg

Object 3:______kg.

13. The person’s push is directed at an angle of θ from the horizontal. She is not pushing up on the box, but merely preventing the stationary box from sliding down. There is friction between the box and the wall.

a Draw a neat, legible, free body diagram for the box with appropriate axes. Label the forces with the correct symbol, listed at the top of page 1.

θ

b. Write Newton’s Law in component form for both the x and y axis. Any vector components should be expressed in terms of sine and cosine.
14.A crate rests on the flatbed of a truck that is initially traveling at 15 m/s on a level road. The driver applies the brakes and the truck is brought to a stop in a distance of 38 m. Assuming the truck slows down at a constant rate, what is the minimum coefficient of friction between the crate and the truck that is required to keep the crate from sliding?

a Draw a neat, legible, free body diagram for this situation with appropriate axes. Label the forces with the correct symbol, listed at the top of page 1.

b. Use Newton’s 2nd Law in component form and any other equations necessary to determine the answer.

15. On a dry day, the maximum velocity with which a car can make it around a circular turn without skidding is 21 m/s. On a rainy day, the coefficient of static friction is reduced by a factor of 3. What is the maximum speed for the same car on this rainy day?

a Draw a neat, legible, free body diagram for this situation with appropriate axes. Label the forces with the correct symbol, listed at the top of page 1.

b. Use Newton’s 2nd Law in component form and ratio reasoning to determine the answer.

1