How many neutrons does element X have if it's atomic number is 21 and it's mass number is 75

An unfortunate astronaut loses his grip during a spacewalk and finds himself floating away from the space station, carrying only a rope and a bag of tools. first he tries to throw a rope to

What is the source of the radioactive nuclei present in spent fuel rods?

The energy of motion?

This theory suggests that for every big bang, there is a big crunch. oscillating universe theory inflation theory steady state theory big bang theory

a cement block accidentally falls from rest from the ledge of a 80.6-m-high building. When the block is 10.8 m above the ground, a man, 2.10 m tall, looks up and notices that the block is directly above him.

A ball of mass 5.0kg is lifted off the floor a distance of 1.7m. 1. What is the change in the gravitational potential energy of the ball? 2. Now you release the ball from rest, and it falls to the floor.

What is the device to break a circuit called?

A 3 column table with 5 rows labeled table A. The first column is labeled voltage in volts with entries 1.0, 5.0, 10, 20, 50. The second column is labeled current: calculated in amps with no entries.

When you stack three flashlight batteries in the same direction, you get a voltage of 3*1.5 volts = 4.5 volts. What voltage do you get if one of the batteries is turned to face in the opposite direction? a) 0 volts b) 1.5 volts c) 3 volts d) - 4.

If an ant were scaled up to the size of an elephant, the ant would be