An object of mass 20 kg moves at a constant speed of `5ms^(-1)`. A constant force, that acts for 2 sec on the object, gives it a speed of `3ms^(-1)` in opposite direction. The force acting on the object is

Options

A. 8N
B. `-80 N`
C. `-8N`
D. 80N

Explanation

To solve the problem, we need to determine the force acting on the object. Here's a step-by-step breakdown of the solution:

### Step 1: Identify the given values
- Mass of the object (m) = 20 kg
- Initial velocity (u) = 5 m/s (in the positive direction)
- Final velocity (v) = -3 m/s (in the opposite direction)
- Time (t) = 2 s

### Step 2: Calculate the acceleration (a)
We can use the formula for acceleration, which is given by:

\[ a = \frac{v - u}{t} \]

Substituting the values:

\[ a = \frac{-3 \, \text{m/s} - 5 \, \text{m/s}}{2 \, \text{s}} = \frac{-8 \, \text{m/s}}{2 \, \text{s}} = -4 \, \text{m/s}^2 \]

### Step 3: Calculate the force (F)
Using Newton's second law of motion, the force can be calculated using the formula:

\[ F = m \cdot a \]

Substituting the values:

\[ F = 20 \, \text{kg} \cdot (-4 \, \text{m/s}^2) = -80 \, \text{N} \]

### Step 4: Interpret the result
The negative sign indicates that the force is acting in the opposite direction to the initial motion of the object.

### Final Answer
The force acting on the object is **80 N** in the opposite direction of the initial motion.

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