What device is used on a power tool's universal motor to provide a burnout-proof motor?
a. current relay
b. circuit breaker
c. thermal protector
d. fuse

Ahot-air balloon takes off from the ground traveling vertically with a constant upward acceleration of magnitude g/4. after time interval δt, a crew member releases a ballast sandbag from the basket attached to the balloon. how many seconds does it take the sandbag to reach the ground? (express your answer in terms of δt)