A set of crash tests consists of running a test car moving at a speed of 10.8 m/s (24.2 mi/hr) into a solid wall. Strapped securely in an advanced seat belt system, a 57.0 kg (126 lbs) dummy is found to move a distance of 0.720 m from the moment the car touches the wall to the time the car is stopped. Calculate the size of the average force which acts on the dummy during that time.

The size of the average force which acts on the dummy during that time=4,617 N

Explanation:

Initial Speed=u= 10.8 m/s

Final Speed=v=0 m/s

Mass=57 kg

distance=s=0.720 m

Required:

The size of the average force which acts on the dummy during that time=?

Solution:

According to 3rd equation of motion

a=-81 m/s^2 (-ve sign for deceleration)

Note:

In calculating the force, we only use the magnitude of acceleration.

According to Newton's Second Equation:

F=ma

F=57*81

F=4,617 N

The size of the average force which acts on the dummy during that time=4,617 N