Question 1:
A ball of mass 5.0 kg hits a smooth vertical wall normally
with a speed of 2 ms^{1} and rebounds with the same speed. Determine
the impulse experienced by the ball.
Solution:
From Newton's second law of motion, Force is directly
proportional to the rate of change of momentum.
I.e. F
= ^{(mv  mu)}/_{t}
Ft = mv
 mu
Where Ft = Impulse (I)
I = mv  mu
Since the speed with which the ball hits the wall is same as
the speed it rebounds with, there is no change in momentum.
Therefore, Impulse (I) is zero, there is no impulse.
Question 2.
A force acts on a body for 0.5 s changing its momentum from
16.0 kgms^{1} to 21.0 kgms^{1}. Calculate the magnitude of the
force.
Solution:
From Newton's second law of motion,
Force equals the rate of change of momentum,
F =
^{(mv  mu)}/_{t}
Where
mv = final momentum,
mu = initial momentum.
F = ^{(21
 16)}/_{0.5}
= 5/0.5
= 10 N
The magnitude of the force is 10 Newtons
Question 3:
A stationary object of mass 4 kg is set in motion by a net
force of 50 N. If the object attains a speed of 5 ms^{1} in time.
Calculate the value of t.
Solution:
From the equation of force,
F = m (vu)/t
Therefore, restating the formula,
t =
m(v  u)/F
Given: mass of object m = 4 kg, final velocity v = 5 ms2,
initial velocity u = 0, Force F = 50 N, t = ?
Hence,
t = 4 x (5  0)/50
= 20/50
t = 0.4s
Question 3.
A force of 100 N is used to kick a football of mass 0.8 kg.
Find the velocity with which the ball moves if it takes 0.8s to be kicked.
Solution:
Using the force equation
F = m (v  u)t
100 = 0.8 (v  0)/0.8
v = 100
The velocity with which the
ball moves is 100 ms1 [Note: initial
velocity, u = 0]
