A force of 20 N acts on a body of mass 5kg at rest. What is the acceleration of the body? What is its velocity after 5 seconds if the same force acts? After 5 seconds if the force ceases to act how will the body move?

Options

A. `4 m//s^(2)`, 20 m/s, uniform velocity
B. `2 m//s^(2)`, 15 m/s , uniform velocity
C. `2 m//s^(2)`, 10 m/s , uniform velocity
D. `4 m//s^(2)`, 20 m/s, uniform acceleration

Answer

To solve the question step by step, we will address each part of the question systematically.

### Step 1: Calculate the acceleration of the body
We know from Newton's second law of motion that:
\[ F = m \cdot a \]
Where:
- \( F \) is the force applied (20 N)
- \( m \) is the mass of the body (5 kg)
- \( a \) is the acceleration

Rearranging the formula to find acceleration:
\[ a = \frac{F}{m} \]

Substituting the values:
\[ a = \frac{20 \, \text{N}}{5 \, \text{kg}} = 4 \, \text{m/s}^2 \]

### Step 2: Calculate the velocity after 5 seconds
We can use the equation of motion to find the final velocity:
\[ v = u + at \]
Where:
- \( v \) is the final velocity
- \( u \) is the initial velocity (0 m/s, since the body is at rest)
- \( a \) is the acceleration (4 m/s²)
- \( t \) is the time (5 seconds)

Substituting the values:
\[ v = 0 + (4 \, \text{m/s}^2 \times 5 \, \text{s}) \]
\[ v = 20 \, \text{m/s} \]

### Step 3: Determine the motion after the force ceases to act
After 5 seconds, if the force ceases to act, the body will continue to move with the velocity it has achieved. According to Newton's first law of motion, an object in motion will remain in motion with a constant velocity unless acted upon by an external force.

Since there is no force acting on the body, it will move with a uniform velocity of 20 m/s.

### Summary of Answers:
1. The acceleration of the body is \( 4 \, \text{m/s}^2 \).
2. The velocity after 5 seconds is \( 20 \, \text{m/s} \).
3. After the force ceases to act, the body will move with a uniform velocity of \( 20 \, \text{m/s} \).