Answer:
The moment is -78.4 N-m (clockwise).
Explanation:
Given:
Mass of the object (m) = 20 kg
Distance of the object from the knee joint (d) = 0.4 m
Weight of leg is not considered.
Acceleration due to gravity (g) = 9.8 m/s²
Now, weight of the object is equal to the product of its mass and acceleration due to gravity. So,
Weight = Mass × Acceleration due to gravity
=
We know that, moment of a force about a point is defined as the product of force applied and the perpendicular distance between the point and the line of application of force.
Moment of the given weight about the knee joint is given as:
Moment about knee joint = Weight × Distance from knee joint to weight
Moment about knee joint = 196 × 0.4 = 78.4 Nm
Now, from the diagram below, we can observe that, the weight acts vertically down and thus the sense of rotation about the knee joint at point O is clockwise. So, moment is negative.
Therefore, the moment is -78.4 N-m (clockwise).
Answer:
14869817.395 m
Explanation:
=22 microarcsecond
λ = Wavelength = 1.3 mm
Converting to radians we get
From Rayleigh Criterion
Diameter of the effective primary objective is 14869817.395 m
It is not possible to build one telescope with a diameter of 14869817.395 m. But, we need this type of telescope. So, astronomers use an array of radio telescopes to achieve a virtual diameter in order to observe objects that are the size of supermassive black hole's event horizon.
Answer:
A. when the mass has a speed of zero
Explanation:
In mass-spring system, the velocity and the acceleration are in anti-phase, which means that when one of the two quantities is maximum, the other one is zero, and vice-versa.
In fact:
- When the displacement of the spring is zero (x=0), the velocity is maximum, due to conservation of energy. In fact, as the displacement is zero, the elastic potential energy of the system (given by ) is zero, therefore the kinetic energy (given by
) must be maximum, and so the velocity (v) is also maximum. On the cotnrary, acceleration (a) is directly proportional to the restoring force of the spring, given by
so we see that when x=0, then the force is zero: F=0, and so the acceleration is zero as well.
- When the displacement of the spring is maximum, the velocity is zero, due to conservation of energy. In fact, as the displacement is maximum, the elastic potential energy of the system (given by ) is maximum, therefore the kinetic energy (given by
) must be zero, and so the velocity (v) is also zero. On the cotnrary, since acceleration (a) is directly proportional to the restoring force of the spring, given by
so we see that when x=maximum, then the force is maximum, and so the acceleration is maximum as well.
Based on this, the correct answer is
A. when the mass has a speed of zero