Apparatus:
Dynamics trolley, tape measure (or 2 x metre rulers), stop-clock, corridor
Diagram:
Procedure:
1. Gently push the trolley away from a known position on the corridor carpet so that it stops after about one metre.
2. Repeat the above but this time use the stop-watch to time, time
how long it takes the trolley to stop and measure how far the trolley travels, the stopping distance
(to the nearest centimetre).
3. Repeat stages 1 & 2 for approximate stopping distances of 25cm, 50cm, 75cm, 1.5m & 2m.
4. Measure the mass,
of the trolley.
5. Calculate time squared
for each of your measurements, then tabulate your results.
6. Draw a graph of stopping distance against time squared.
For a constant frictional force,
the graph is expected to be a straight line through the origin.
(Do not worry if you in fact obtain a curve that does not pass through the origin!)
7. Calculate the gradient,
of your graph.
(Note: If you have drawn a curve then calculate the gradient of the tangent to your curve for a stopping distance of 1 metre.)
8. According to theory the work done by a constant retarding frictional forceapplied for a distance
is equal to the initial kinetic energy of the trolley,
i.e.
Also if the trolley's deceleration is uniform then
(
)
Combining the above two equations yields
9. The gradient,of your graph should therefore be equal to
Use your gradient value to calculate the value of the retarding force
10. Use the above calculations and your graph to find for a stopping distance of 1m:
(a) the stopping time
(b) the initial velocity
(c) the power needed to maintain this velocity by a motor mounted on the trolley.
(you need to use the relation: power = force x velocity here)
(d) Explain why the power actually needed by the motor would in fact be substantially higher than that above.