Question

15. Two horizontal forces (5N)i-(10N)j and (7N)i+(12N)j are acting on an object. What is direction of object’s acceleration?

a. in positive x direction

b. in negative x direction

c. in positive y direction

d. in negative y direction

e. 45⁰ from positive x direction.

f. 45⁰ from negative x direction.

16. You press a book of mass m against vertical wall with a force F big enough to prevent book from sliding.

1.1 What force acts against possible direction of sliding of a book?

a. Gravity

b. Normal force

c. Force of friction

d. Force F.

1.2 What is magnitude and direction of normal force?

a. mg perpendicular to the wall

b. mg vertically up

c. F vertically up

d. F perpendicular to the wall.

e. Impossible to answer from the information given.

1.3 What is magnitude of force of friction in given situation?

a. mg

b. F

c. slightly less than mg

d. slightly greater than mg

e. Impossible to answer from the information given.

Answer 1

15) Answer : a) in positive x- direction

Explanation: The following calculations show that the acceleration would be inclined at an angle of 9.462^o from the positive x axis. The closest option is "a) in positive x- direction", else none of the options are correct.

16)

1.1 What force acts against possible direction of sliding of a book?

Answer: Option c) Force of friction

Explanation: From the free body diagram we can clearly see the frictional force opposing the sliding of the book.

1.2 What is magnitude and direction of normal force?

Answer: Option d) F perpendicular to the wall

Explanation: From the free body diagram, the normal reaction is found to be equal and opposite to "F" for the book to be in static equilibrium.

1.3 What is magnitude of force of friction in given situation?

Answer: Option a) mg

Explanation: From the free body diagram, we can conclude that the frictional force must be greater than or equal to the weight of the book (mg). But as the force "F" is sufficient to hold the book in place so it can be exactly equal to "mg".