A theatre crew uses a winch to move a wheeled scenery platform along a straight, level stage.
The empty platform has a mass of 180 kg and carries scenery of mass 120 kg. At the start of the test, the platform has a velocity of 0.50 m/s forwards.
The forces on the platform during the test are shown in the table.
| Time interval in s | Pulling force forwards in N | Resistive force backwards in N |
|---|---|---|
| 0.0 to 4.0 | 150 | 60 |
| 4.0 to 7.0 | 30 | 120 |
Calculate the velocity of the platform after 7.0 s.
In a second test, the 120 kg scenery is replaced by a prop of mass 60 kg. The pulling force is 132 N forwards and the resistive force is 60 N backwards.
Calculate the acceleration of the platform.
Compared with the first 4.0 s of the first test, the total mass is smaller in (b). Explain why this does not produce a greater acceleration.