A child of mass 40 kg jumps off a wall and hits the ground at 4 m/s. He bends his knees and stops in 1s. Calculate the force required to slow him down. How would this force be different if he didn't bend his knees and stopped in 0.1s ?
Answers
KE = Ft
Solve for F
his acceleration is 4m/s^2
F = ma
1/10 the time means 10 times the acceleration.
Answer:
1600N
Explanation:
force applied at 1s: 160N
force would increase to 1600N at 0.1s
Explanation:
F=mΔvt
force = mass * change in velocity / time
at 1s:
mass: 40kg
change in velocity (taking downwards as a positive direction):
4 m/s to rest =4−0=4 m/s
time: 1 s
mΔvt=1601=160
force applied =160N
at 0.1s:
mΔvt=1600.1=1600
force applied = 1600N
note that in the equation for force applied, time is the denominator.
this means that force is inversely proportional to time - as force increases, time decreases, and vice versa.
if the time is divided by a certain amount, the new force can be found by multiplying the previous force by that same amount.
here, dividing the time by 10, from 1s to 0.1s, multiplies the force by 10, from 160N to 1600N.