Physics Dynamics

Question

5. A 1000-kg sports car accelerates from rest with an acceleration of 3.2 m/s2. Calculate the net force acting on the car.

6. During a head on collision, the person in the front seat of a car decelerates from 13.3 m/s (30 mi/hr) to rest in 0.10 seconds. If the persons mass is 75-kg(165 lb), calculate the average force of the seat belt and shoulder strap on the person.

7. A 0.15-kg baseball enters the glove of a catcher at a speed of 92 mi/hr. Calculate the average force of the glove on the ball, assuming constant deceleration.

8. A rope will break if its tension exceeds 3000N. Calculate the minimum time needed to pull with this rope a 1400-kg car from rest to a speed of 15 m/s. Ignore friction.

Answer 1

For #5, Force = mass * acceleration

F = ?

m = 1000 kg

a = 3.2 m/s^2

F = 1000*3.2

F = 3200 N

For #6 we may assume that the shoulder strap and seat belt are the only objects applying the force that decelerates the person.

acceleration = Δv / Δt

Δv = 13.3 m/s

Δt = .1 s

a = 13.3 / .1 = 133 m/s^2

Force = mass * acceleration

F = ?

m = 75 kg

a = 133 m/s^2

F = 75 * 133

F = 9975 N

For number 7, the time the baseball took to decelerate is also needed to solve the problem. It will then be plugged into:

F_avg = m * (v_f - v_i) / t

F_avg = ?

m = .15 kg

v_f = 0 m/s

v_i = 92 mi/hr = 41.13 m/s

t = ?

F_avg = .15 * (-41.13) / t

For number 8, Force = mass * acceleration

F = 3000 N

m = 1400 kg

a = ?

3000 = 1400 * a

a = 2.14 m/s^2

acceleration = Δv / Δt

a = 2.14 m/s^2

Δv = 15 m/s

Δt = ?

2.14 = 15 / Δt

t = 7s