Question:
A 63.0 kg sprinter starts a race with an acceleration of 4.20m/s square. What is the net external force on him? If the sprinter from the previous problem accelerates at that rate for 20m, and then maintains that velocity for the remainder for the 100-m dash, what will be his time for the race?
Answer:
Time for the race will be t = 9.26 s
Explanation:
Given data:
As the sprinter starts the race so initial velocity = v₁ = 0
Distance = s₁ = 20 m
Acceleration = a = 4.20 ms⁻²
Distance = s₂ = 100 m
We first need to find the final velocity (v₂) of sprinter at the end of the first 20 meters.
Using 3rd equation of motion
(v₂)² - (v₁)² = 2as₁ = 2(4.2)(20)
v₂ = 12.96 ms⁻¹
Time for 20 m distance = t₁ = (v₂ - v ₁)/a
t₁ = 12.96/4.2 = 3.09 s
He ran the rest of the race at this velocity (12.96 m/s). Since has had already covered 20 meters, he has to cover 80 meters more to complete the 100 meter dash. So the time required to cover the 80 meters will be
Time for 100 m distance = t₂ = s₂/v₂
t₂ = 80/12.96 = 6.17 s
Total time = T = t₁ + t₂ = 3.09 + 6.17 = 9.26 s
T = 9.26 s
Energy is the ability to do work.<span />
Answer:571.09 kJ
Explanation:
Given
Temperature of cooling water from engine exit
After Passing through the radiator its temperature decreases to 
specific heat of water
Volume of water 
density of water 
Thus mass of water
Heat transferred to the surrounding is equal to heat absorbed by cooling water




To determine the Force it is necessary that Samantha starts from the consideration of the dynamic balance between the forces acting on the car. For this, the centripetal force must be equal to the friction force (otherwise the car would lose contact with the ground), the expression of these two forces would be


Here,
= Coefficient of kinematic friction
m = mass
g = Acceleration due to gravity
v = Velocity
r = Radius
From this relationship then she should assume the following
1) The car travels at a constant speed
2) There is indeed that frictional force between the car and the road
3) There is no loss of mass during displacement
4) The centripetal force must be equal to the frictional force so that the car does not lose contact or slip
5) The radius must be constant
It is definitely temerature.
Hoped this helped. :)