Answer:
Vf = 73.4 m/s
Explanation:
This is the case of vertical motion where we have to find the final velocity of the penny when it hits the ground. We can use 3rd equation of motion to find the final velocity:
2gh = Vf² - Vi²
where,
g = 9.8 m/s²
h = height = 275 m
Vf = Final Velocity = ?
Vi = Initial Velocity = 0 m/s
Therefore,
2(9.8 m/s²)(275 m) = Vf² - (0 m/s)²
Vf = √5390 m²/s²
<u>Vf = 73.4 m/s</u>
Answer:
B) A stack of books is carried at waist level across a room
Explanation:
Work is defined as:

where
F is the force applied
d is the displacement of the object
is the angle between the direction of the force and of the displacement
From the formula, we see that the work done is zero when the force and the displacement are perpendicular to each other. Let's now analyze each situation:
A) A bookcase is slid across carpeting. --> work is done, because the force that pushes the bookcase is in the same direction of the displacement
B) A stack of books is carried at waist level across a room. --> no work is done, because the force to carry the book is vertical, while the displacement of the books is horizontal
C) A chair is lifted vertically with respect to the floor. --> work is done, because the force that lifts the chair is vertical, and the displacement is vertical as well
D) A table is dropped onto the ground. --> work is done, because the force of gravity (that makes the table falling down) is vertical and the displacement of the table is also vertical.
Answer:


Explanation:
Given that.
Force acting on the particle, 
Position of the particle, 
To find,
(a) Torque on the particle about the origin.
(b) The angle between the directions of r and F
Solution,
(a) Torque acting on the particle is a scalar quantity. It is given by the cross product of force and position. It is given by :




So, the torque on the particle about the origin is (32 N-m).
(b) Magnitude of r, 
Magnitude of F, 
Using dot product formula,




Therefore, this is the required solution.