- #1

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## Homework Statement

A toy car of mass 0.5 kg works with a wound spring that exerts a force as shown in the table below.The car was initially at rest. The spring is wound at the car set in motion on a horizontal surface.

t = 0 s ------> F = 0.2 N

t = 1 s ------> F = 0.18 N

t = 2 s ------> F = 0.15 N

t = 3 s ------> F = 0.12 N

t = 4 s ------> F = 0.1 N

t = 5 s ------> F = 0.08 N

t = 6 s ------> F = 0.05 N

t = 7 s ------> F = 0.02 N

t = 8 s ------> F = 0 N

a. Plot the graph of force vs time using the table above. Determine from the graph the speed of the car 8 s after being released.

b. The car then crashes into a stationary car of mass 1.5 kg and is stuck to the second car. Calculate the speed of the two cars after collision. Show if the collision is elastic or not

## Homework Equations

1. p = Ft

2. conservation of momentum

**3. attempt at a solution**

a.

I'm not sure how to find the speed from the graph. The best I can try is I assume the graph is triangle, then I find the area which is equal to change in momentum.

Area = change in momentum

0.5*0.2*8 = mv

v = 1.6 ms

^{-1}

b. m

_{1}u

_{1}+m

_{2}u

_{2}=(m

_{1}+m

_{2})V

0.5*1.6 = (0.5 + 1.5) V

V = 0.4 ms

^{-1}

The collision is perfectly inelastic

Am I right ?

Thanks