Answer:
7revolutions
Explanation:
Given parameters:
Initial revolution = 250rpm
Final revolution = 150rpm
Time = 4.2s
Unknown:
Number of revolutions that occur at this time = ?
Solution:
To solve this problem;
let us find the change in revolution = 250rpm - 150rpm = 100rpm
Convert the time to seconds;
60s makes 1 minute
4.2s will make 
= 0.07min
So;
The number of revolutions at this time = 100rpm x 0.07min
= 7revolutions
Answer:
A north magnet attracts a south magnet
Explanation:
The opposite polar magnetic field will attract each other while the same polar magnetic fields will repel each other.
KE = 0.5mV^2 = 0.5 * 0.0025 * (20)^2 =
<span>0.5 Joules.</span>
Answer:
F = 24 N
Explanation:
In this exercise we have a bar l = 100 m with a center of gravity x = 4 m, which force is needed to lift it from the other end
Let's use the rotational equilibrium relationship, where we consider the counterclockwise rotations as positive and fix the reference system at the point closest to the center of gravity
∑ τ = 0
F l -x W = 0
F = 
let's calculate
F = 
4/100 600
F = 24 N
