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 crate moves at constant velocity, this means that its acceleration is zero, so the net force acting on the crate is zero (Newton's second law).
There are only two forces acting on the crate: the force F applied by the worker and the frictional force, acting in the opposite direction:
, where
is the coefficient of friction and
is the mass of the crate. Since the net force should be equal to zero, the two forces must have same magnitude, so we have:
And so, this is the force that the worker must apply to the crate.
At normal temperature,
specific heat of air = 1.006
concrete =0.96
water =4.187 (all are in KJ/KgK)
soil = 0.80
So, from <span>Q=mcDeltaT</span><span>
higher the specific heat lower the change in temperature for same quantity of heat supplied.
Therefore, water is the answer.</span>
A= 50/8 m/s^2
<span>vf=at=50/8 * 5= 250/8 m/s at t=5sec </span>
<span>time to get to 50m/s </span>
<span>50=50/8*t or t=8 seconds </span>
<span>distance=1/2 a t^2=1/2 50/8 64 </span>
<span>distance= 400 m check that.</span>
