To solve the problem, we need to determine the reading on the weighing scale when the man is in a lift that is accelerating upwards.
### Step-by-Step Solution:
1. **Identify the Forces Acting on the Man:**
- The weight of the man (W) acts downwards, which can be calculated using the formula:
\[
W = mg
\]
- The normal force (N) exerted by the weighing scale acts upwards.
2. **Calculate the Weight of the Man:**
- Given that the mass (m) of the man is 80 kg and taking the acceleration due to gravity (g) as approximately \(10 \, \text{m/s}^2\):
\[
W = 80 \, \text{kg} \times 10 \, \text{m/s}^2 = 800 \, \text{N}
\]
3. **Apply Newton's Second Law:**
- Since the lift is moving upwards with an acceleration (a) of \(5 \, \text{m/s}^2\), we can apply Newton's second law. The net force (F_net) acting on the man can be expressed as:
\[
F_{\text{net}} = N - W
\]
- According to Newton's second law, this net force is also equal to the mass times the acceleration:
\[
F_{\text{net}} = ma
\]
4. **Set Up the Equation:**
- Combining the two expressions for net force, we have:
\[
ma = N - W
\]
- Rearranging gives:
\[
N = ma + W
\]
5. **Substitute the Known Values:**
- Now substitute the values into the equation:
- Mass (m) = 80 kg
- Acceleration (a) = \(5 \, \text{m/s}^2\)
- Weight (W) = \(800 \, \text{N}\)
\[
N = (80 \, \text{kg} \times 5 \, \text{m/s}^2) + 800 \, \text{N}
\]
- Calculate:
\[
N = 400 \, \text{N} + 800 \, \text{N} = 1200 \, \text{N}
\]
6. **Conclusion:**
- The reading on the scale, which is the normal force (N), is \(1200 \, \text{N}\).
### Final Answer:
The reading on the scale would be **1200 N**.
