Answer: 
Explanation:
where;
= final velocity = 0
= initial velocity = 60 km/h = 16.67 m/s
= acceleration
= distance
First all of, because acceleration is given in m/s and not km/h, you need to convert 60km/h to m/s. Our conversion factors here are 1km = 1000m and 1h = 3600s
Solve for a;
Begin by subtracting 
Divide by 2d
Now plug in your values:
If you're wondering why I calculated acceleration first is because in order to find force, we need 2 things: mass and acceleration.
m = mass = 900kg
a = acceleration = -2.78m/s
It's negative because the force has to be applied in the opposite direction that the car is moving.
Answer:
29 seconds
Explanation:
First we have a constant speed of 12 m/s and the distance of 240 m, so to find the time we can use the formula:
distance = speed * time
240 = 12 * time1
time1 = 20 seconds
Then, the speed decreases at 2 m/s2 until it reaches 2 m/s. So to find this time, we use this formula:
Final speed = inicial speed + acceleration * time
2 = 12 - 2 * time2
2*time2 = 10
time2 = 5 seconds.
Then, the speed increases from 2 m/s to 22 m/s with an acceleration of 5 m/s2, so we have:
Final speed = inicial speed + acceleration * time
22 = 2 + 5 * time3
5*time3= 20
time3 = 4 seconds
The total time is:
Total time = time1 + time2 + time3 = 20 + 5 + 4 = 29 seconds
In case of an object sitting at rest on another base, there are two equal and opposite forces – Normal force and the gravity.
Answer: Option A
<u>Explanation:
</u>
When an object is placed at rest position on another object, there is a force exerted by the surfaces of the two contact objects. This force is denoted as Normal Force.
When an object such as a box is placed on a shelf, its surface exerts a contact force on the base of the shelf- The Normal force directed upward. Meanwhile, the gravity stays at its action and tries to pull the box towards itself.
Both of these forces however are equal and opposite and therefore, there is zero net force on the box. That's why it remains at rest, holding on Newton's third law.
Answer:
It can be shown that the potential energy of an object at the surface of the planet would be -G M / R if the potential at infinity is chosen to be zero.
Kinetic energy of G M / R would be required for the escape speed of such an object. The total energy in all such cases is zero.
This can easily be seen by considering the speed of an object falling from infinity towards the planet - the total energy will remain zero if it was zero when the object started to fall.
