Explanation:
Given that,
Force acting on the child, F = 310 N
Length of the ropes, d = 2.1 m
We need to find the gravitational potential energy of the child–Earth system relative to the child's lowest position when the ropes are horizontal. The potential energy is simply given by :

Hence, this is the required solution.
The only way to decrease the inertia of an object is to remove some of its mass. (B)
Answer:
F = 0.84 [N]
Explanation:
In order to solve this problem we must take into account Newton's second law, which tells us that the sum of all forces applied on a body must be equal to the product of the mass of the body by its acceleration.
F = m*a
where:
F = force [N]
a = acceleration = 1.4[m/s^2]
m = mass = 0.6 [kg]
F = 0.6*1.4
F = 0.84 [N]
The bus and the truck have the same velocity.
Also, Valerie and Owen have the same velocity.
Answer: Heart can beat 140 times in = 2 minutes