Answer:
Pebble A has 1/3 the acceleration as pebble B.
Explanation:
F = m×a
mass of a = 3 × mass of b (m_a = 3 × m_b)
Same starting force, F
m_a = mass of a
m_b = mass of b
a_a = acceleration of a
a_b = acceleration of b
F = m_a × a_a = m_b × a_b
3 × m_b × a_a = m_b × a_b
3 × a_a = a_b
OR
a_a = a_b / 3
Answer:
1.95 kg
Explanation:
Momentum is conserved.
m₁ u₁ + m₂ u₂ = m₁ v₁ + m₂ v₂
0 = (74.9) (-0.215) + m (8.25)
m = 1.95
A) 
The total energy of the system is equal to the maximum elastic potential energy, that is achieved when the displacement is equal to the amplitude (x=A):
(1)
where k is the spring constant.
The total energy, which is conserved, at any other point of the motion is the sum of elastic potential energy and kinetic energy:
(2)
where x is the displacement, m the mass, and v the speed.
We want to know the displacement x at which the elastic potential energy is 1/3 of the kinetic energy:

Using (2) we can rewrite this as

And using (1), we find

Substituting
into the last equation, we find the value of x:

B) 
In this case, the kinetic energy is 1/10 of the total energy:

Since we have

we can write

And so we find:
