Question

The body is at rest. Under the action of a constant force of 30 N after 4 s, its kinetic energy is 720 J. What is the speed of the body then?​

Answer 1

12 m/s

Step-by-step explanation:

KE = kinetic energy/J

I = impulse/Ns

m = mass/kg

v = final velocity/ms⁻¹

u = starting velocity/ms⁻¹ = 0

KE = ¹/₂mv²

ΔKE = ¹/₂mv² - ¹/₂mu²

ΔKE = ¹/₂mv² = 720

I = 30 × 4

I = 120 = mv - mu → impulse-momentum principle

mv = 120

`m = (120)/(v)`

Substitution:

`(1)/(2)((120)/(v)) v^(2) = 720 \\\\ 60v = 720 \\\\ v = 12`