Question 1: At a given instant in time, a 10-kg rock is observed to be falling w

Question

Question 1:

At a given instant in time, a 10-kg rock is observed to be falling with an acceleration of 8.5 m/s2. What is the magnitude of the force of air resistance acting upon the rock at this instant?

Answer:

Question 2:

A 0.5-kg book rests on a table. A downward force of 9 N is exerted on the top of the book by a hand pushing down on the book.

a. What is the magnitude of the gravitational force acting upon the book?

b. What is the magnitude of the upward (normal) force exerted by the table on the book? (Is the book accelerated?)

Question 3:

A rope exerts a constant horizontal force of 280 N to pull a 50-kg crate across the floor. The velocity of the crate is observed to increase from 1 m/s to 7 m/s in a time of 2 seconds under the influence of this force and the frictional force exerted by the floor on the crate.

a. What is the acceleration of the crate?

b. What is the net force acting upon the crate?

c. What is the magnitude of the frictional force acting on the crate?

d. What force would have to be applied to the crate by the rope in order for the crate to move with constant velocity? Explain.

Explanation / Answer

1) g = 9.8m/s2

a = 8.5m/s*s

hence resistive acceleration = 9.8-8.5 = 1.3

hence force = 10*1.3 = 13N

2)a) gravitation force on the book = 0.5*9.8 = 4.9N

b) upward force exerted by the table = gravitatoinal force + pushing force = 4.9+ 9 =13.9N

3) a) a =7-1/2 =6/2 = 3m/s2

b) net force= a*mass = 3*50 = 150N

c) hence frictional force = 280 - 150 = 130N

d) force applied for constant velocity = frictional force + gravitaiotnal force = 50*9.8+150 = 640N

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