A barefoot field-goal kicker imparts a speed of 30 m/s to a football at rest.If the football has a mass of 0.45 kg and time of contact with the football is 0.035 s,what is the force exerted on the foot?
A)14 N
B)13 N
C)390 N
D)860 N
E)900 N

Question

Quizplus · Accepted Answer

Using the formula for impulse:
impulse = force x time
And the formula for initial velocity:
v = u + at
where u = 0 since the football is at rest
a = F/m (Newton's second law)
t = 0.035 s
v = 30 m/s

Substituting the values:
impulse = Ft = 0.45 x 30
impulse = 13.5 Ns

Therefore, force exerted on the foot:
F = impulse/time = 13.5/0.035
F = 385.7 N ≈ 390 N (to 2 significant figures)

A Barefoot Field-Goal Kicker Imparts a Speed of 30 M/s