Question

You push a plump 65N Violet distance of 60.0m at a constant velocity for 25s by exerting a 145N force horizontally.
Givens: Draw a FBD representing the direction of the influencing
force, also note the direction of motion
What is the force applied?
What work is done? How much power are you
putting out?
If they move the Violet twice as
fast, how would the power be affected?

Answer 1

First the free-body diagram (FBD), with motion to the right:
- Applied force: 145 N → (right)
- Friction (or resistive) force: 145 N ← (left) — equal and opposite so velocity is constant
- Weight: 65 N ↓
- Normal: 65 N ↑

Answers and calculations
1. What is the force applied?
- 145 N horizontally to the right.

2. What work is done?
- Work by the applied force = F·d = 145 N × 60.0 m = 8 700 J.
- (Work by friction = −8 700 J, so the net work = 0 because constant velocity.)

3. How much power are you putting out?
- Average power = work / time = 8 700 J / 25 s = 348 W.
- (Also P = F·v = 145 N × (60/25 m/s = 2.4 m/s) = 348 W.)

4. If they move the Violet twice as fast, how is power affected?
- Power is proportional to speed for the same horizontal force: P = F v. Doubling the speed doubles the power.
- So the power would be 2 × 348 W = 696 W.