Explanation:
When a constant force acts upon an object the acceleration of the object varies inversely with its mass.

or

If m₁ = 21 kg, a₁ = 3 m/s², m₂ = 9 kg
We need to find a₂
So,

So, if mass is 9 kg, its acceleration is 7 m/s².
Answer:
2.1 s
Explanation:
The motion of the ball is a projectile motion. We know that the horizontal range of the ball is

And that the initial speed of the ball is

at an angle of

So, the horizontal speed of the ball (which is constant during the entire motion) is

And since the horizontal range is 50 m, the time taken for the ball to cover this distance was

which is the time the ball spent in air.
Answer:
Because it is made by two different unit force (F) and displacement(s)