60 km/h car will kill you either way, 1 km/h car won't kill you either way, but somewhere in between there's a velocity range where a SUV will kill you and a compact car won't - simply because of the mass difference. I'd argue it's the velocity range in which a lot of collisions happen (especially in city traffic).
Both objects have an overwhelming amount of energy and momentum compared to a nearly stationary 100 kg person. They'll transfer enough energy to bring the person up to their speed, likely mangling them in the process.
Trauma depends on how quickly this energy is transferred to the individual.
More to your point, both a car and a truck have more than enough energy to not be meaningfully slowed down by a pedestrian. The difference is strike location, contact area, and crumple zones to slow the transfer.
X_p0 = X of the pedestrian before collision
X_c0 = X of the car before collision
X_p1 = X of the pedestrian after the collision
X_c1 = X of the car after the collision
m_ = mass
v_ = velocity
a_ = acceleration
t = time
//conservation of momentum:
m_p * v_p0 + m_c * v_c0 = m_p * v_p1 + m_c * v_c1
m_p * (v_p0 - v_p1) = m_c * (v_c1 - v_c0)
v_p1 - v_p0 = m_c * (v_c0 - v_c1) / m_p
// a = delta v / t
a = (v_p1 - v_p0)/t = m_c * (v_c0 - v_c1) / (m_p * t)