physics homework plz help

Question

A 2.00 kg block hangs from a spring balance calibrated in Newtons that is attached to the ceiling of an elevator.

(a) What does the balance read when the elevator is ascending with a constant speed of 27 m/s? 

 N 

(b) What does the balance read when the elevator is descending with a constant speed of 33 m/s? 

 N 

(c) What does the balance read when the elevator is ascending at 34 m/s and gaining speed at a rate of 7 m/s²? 

 N 

(d) Suppose that from t = 0 to t = 4.3 s, the elevator ascends at a constant speed of 10 m/s. Its speed is then steadily reduced to zero during the next 4.0 s, so that it is at rest at t = 8.3 s. Describe the reading of the scale during the interval 0 < t < 8.3 s.

T0 → 4.3 =	N
T4.3 → 8.3 =	N

Answer 1

We first consider the forces acting on the block. We have the tension force T pointing up and the gravitational force mg pointing down.

Using Newton's 2nd law we can write T - mg = ma ⇒ T = m(g+a). We are interested in the value of T in these various conditions.

We note that a constant velocity means a = 0 ⇒ T = mg. However, T > mg when a > 0 and T < mg when a < 0. You can find exactly what T is in these situations by plugging in values.