I do not agree with the statement.
The "substance" can be a compound. It's "pure"
as long as there's nothing else in it but its name.
'Pure' water is 100% H₂O with nothing else in it.
'Pure' table salt is 100% NaCl with nothing else in it.
'Pure' carbon dioxide is 100% CO₂ with nothing else in it.
These example substances are all compounds, not elements.
Answer:
D) 11 m/s
Explanation:
The problem asks us to calculate the velocity of the hot dog with respect to the observer stationary outside the train. This velocity is given by:

where
is the velocity of the train (towards right)
is the velocity of the man (towards right)
is the velocity of the hot-dog (towards left, so we put a negative sign)
Substituting the numbers into the equation, we find

and the positive sign means the velocity is toward right.
Answer:
P = 227 N
Explanation:
Assuming the crate is on horizontal ground and subject to a horizontal force.
F = ma
P - μmg = ma
P = m(a + μg)
P = m(v²/2s + μg)
P = 50(4²/(2(5))+ 0.3(9.8))
P = 227 N
Answer:
v = 2,425 m / s
Explanation:
A simple pendulum has anergy stored at the highest point of the path and this energy is conserved throughout the movement.
highest point
Em₀ = U = m g y
lowest point
= K = ½ m v²
Em₀ = Em_{f}
mg y = ½ m v²
v = √ 2gy
let's calculate
v = √ (2 9.8 0.3)
v = 2,425 m / s