Use the equations for momentum and kinetic energy to derive an expression for the kinetic energy Ek of a particle in terms of its momentum p and mass m.
Fig. 20.1 shows an electric motor used to lift and lower a load.
Fig. 20.1
At time t = 0 the load is on the ground with displacement s = 0.
Fig. 20.2 shows the variation of the displacement s of the load with time t.
Fig. 20.2
Fig. 20.3
i) On Fig. 20.3, sketch a graph to show the variation of the velocity v of the load with time t.
You do not need to insert a scale on the v axis.
[3]
ii) Describe how the kinetic energy and the gravitational potential energy of the load varies from t = 0 to t = 2.0 s.
[2]
iii) During the downward journey of the load, the string breaks at t = 4.0 s. It then falls vertically toward the ground. The mass of the load is 120 g.
Air resistance is negligible.
1. Calculate the velocity V of the load just before it hits the ground.
V = ................................................ m s−1 [2]
2. The load hits the ground and comes to rest in a time interval of 25 ms.
Calculate the average force F exerted by the ground on the load.
F = ...................................................... N [2]
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