Scientists are experimenting with a kind of gun that may eventually be used to fire payloads directly into orbit. In one test, this gun accelerates a 3.8-kg projectile from rest to a speed of 9.3 × 103 m/s. The net force accelerating the projectile is 9.3 × 105 N. How much time is required for the projectile to come up to speed?

Explanation:

Project mass m=3.8 kg

Initial speed vi= 0m/s

Final speed vf= 9.3×10³ m/s

Force F=9.3×10⁵N

To find

Time t

Solution

From Newtons second law we know that

∑F=ma

Where m is mass

a is acceleration

We can write this equation as

∑F=m(Δv/Δt)

Rearrange this equation to find time t

So

Substitute the given values

explanation:

v=uf/(u-f)

= 5.-10/(5+10) convex lens has negative focal length

air exerts forces on falling objects near earth’s surface.

explanation:

the term 'free falls' refer to object that are falling towards the earth, in a situation in which gravity is the only force acting on the object.

for an object in free fall, the acceleration is constant (g, the gravitational acceleration), and so the velocity of the object constantly increases.

for objects near earth's surface, there is always another force acting on the object: the resistance due to the air. this force is opposed to the direction of fall of the object, and it is proportional to the velocity of the object, so as the object falls down, this force increases up to a point when it balances the force of gravity, and the object continues its motion at constant velocity (called terminal velocity). since in this case gravity is not the only force acting on the object, we are not in a situation of free fall.