forces and motion

Question 1

State the formula linking momentum, mass and velocity

Answer 1

momentum = mass × velocity;

Question 2

The dummy is brought to rest during the collision by a mean force of 15kN.
Calculate the time taken for the dummy to be brought to rest in the collision.

Answer 2

F = ∆p / t;
∆p = F x t

Question 3

Using ideas about momentum, explain how an airbag reduces the force
experienced by the dummy in the collision.

Answer 3

idea that airbag increases the (collision) time;
reduces the rate of change of momentum;

Question 4

The mass of the racing car is 830kg.
The maximum braking force is 41000N.
Show that the maximum deceleration of the racing car is
approximately 50m/s
2.

Answer 4

force = mass × acceleration;

substitution and rearrangement;
F = m × a
a = 41000 / 830
a = 49 (m/s2)

Question 5

The racing car is travelling at an initial speed of 72m/s.
Calculate the minimum distance needed to decrease the speed of the racing
car from 72m/s to 26m/s.

Answer 5

substitution into v2 = u2 + 2as;
rearrangement;
evaluation;
e.g.
262 = 722 + 2×(-50)×s
(distance =) 5184-676 / 100
(distance =) 45 (m)

Question 6

An extension-force graph has a straight sloped/diagonal line. what is it showing

Answer 6

idea that extension increases as force
increases;

idea of a linear relationship;

Question 7

The force the spring exerts on the gate is 480N.
Show that the moment of the force the spring exerts on the gate is about 400Nm

Answer 7

moment = force × distance;
moment = 480 × (0.)84
moment = 403 (Nm)

Question 8

The spring is removed for testing.
Explain what will happen to the spring if the force applied to extend the spring is
too larg

Answer 8

idea of spring exceeding/reaching elastic
limit/limit of proportionality;

idea of permanent deformation / not returning

to original shape / permanent stretching;