Answer:
Speed of the ball relative to the boys: 25 km/h
Speed of the ball relative to a stationary observer: 35 km/h
Explanation:
The RV is travelling at a velocity of

Here we have taken the direction of motion of the RV as positive direction.
The boy sitting near the driver throws the ball back with speed of 25 km/h, so the velocity of the ball in the reference frame of the RV is

with negative sign since it is travelling in the opposite direction relative to the RV. Therefore, this is the velocity measured by every observer in the reference frame of the RV: so the speed measured by the boys is
v = 25 km/h
Instead, a stationary observer outside the RV measures a velocity of the ball given by the algebraic sum of the two velocities:
v = +60 km/h + (-25 km/h) = +35 km/h
So, he/she measures a speed of 35 km/h.
The length of the wire is 36 m.
<u>Explanation:</u>
Given, Diameter of sphere = 6 cm
We know that, radius can be found by taking the half in the diameter value. So,

Similarly,

We know the below formulas,


When equating both the equations, we can find length of wire as below, where 


The
value gets cancelled as common on both sides, we get

The
value gets cancelled as common on both sides, we get

Explanation:
Coefficient of kinetic friction is the resistive force that opposes the motion of a body as it moves and is in contact with another body.
It is found by dividing the frictional force by the normal force.
- Friction is a force that opposes motion.
- Static friction is for bodies that are not in motion
- Kinetic friction is for moving bodies.